In molecular biology miR-203 is a short

non-coding RNA A non-coding RNA (ncRNA) is a functional RNA molecule that is not Translation (genetics), translated into a protein. The DNA sequence from which a functional non-coding RNA is transcribed is often called an RNA gene. Abundant and functionally imp ...

molecule.

MicroRNA Micro ribonucleic acid (microRNA, miRNA, μRNA) are small, single-stranded, non-coding RNA molecules containing 21–23 nucleotides. Found in plants, animals, and even some viruses, miRNAs are involved in RNA silencing and post-transcr ...

s function to regulate the expression levels of other genes by several mechanisms, such as translational repression and

Argonaute The Argonaute protein family, first discovered for its evolutionarily conserved stem cell function, plays a central role in RNA silencing processes as essential components of the RNA-induced silencing complex (RISC). RISC is responsible for the ...

-catalyzed

messenger RNA In molecular biology, messenger ribonucleic acid (mRNA) is a single-stranded molecule of RNA that corresponds to the genetic sequence of a gene, and is read by a ribosome in the process of synthesizing a protein. mRNA is created during the ...

cleavage. miR-203 has been identified as a

skin Skin is the layer of usually soft, flexible outer tissue covering the body of a vertebrate animal, with three main functions: protection, regulation, and sensation. Other animal coverings, such as the arthropod exoskeleton, have different ...

-specific microRNA, and it forms an expression gradient that defines the boundary between proliferative

epidermal The epidermis is the outermost of the three layers that comprise the skin, the inner layers being the dermis and hypodermis. The epidermal layer provides a barrier to infection from environmental pathogens and regulates the amount of water relea ...

basal progenitors and terminally differentiating suprabasal cells. It has also been found upregulated in

psoriasis Psoriasis is a long-lasting, noncontagious autoimmune disease characterized by patches of abnormal skin. These areas are red, pink, or purple, dry, itchy, and scaly. Psoriasis varies in severity from small localized patches to complete b ...

and differentially expressed in some types of

cancer Cancer is a group of diseases involving Cell growth#Disorders, abnormal cell growth with the potential to Invasion (cancer), invade or Metastasis, spread to other parts of the body. These contrast with benign tumors, which do not spread. Po ...

Introduction

MicroRNAs are short (20-22nt), non-coding RNA molecules involved in the regulation of messenger RNAs (mRNAs) by pairing with their 3' UTR and affecting their stability or directing their silencing or degradation. MicroRNAs are likely to play roles in most cellular processes, including proliferation, development, differentiation and

apoptosis Apoptosis (from ) is a form of programmed cell death that occurs in multicellular organisms and in some eukaryotic, single-celled microorganisms such as yeast. Biochemistry, Biochemical events lead to characteristic cell changes (Morphology (biol ...

. They are located in intergenic and intragenic regions, and are transcribed as pri-miRNA by

RNA polymerase II RNA polymerase II (RNAP II and Pol II) is a Protein complex, multiprotein complex that Transcription (biology), transcribes DNA into precursors of messenger RNA (mRNA) and most small nuclear RNA (snRNA) and microRNA. It is one of the three RNA pol ...

RNA polymerase III In eukaryote cells, RNA polymerase III (also called Pol III) is a protein that transcribes DNA to synthesize 5S ribosomal RNA, tRNA, and other small RNAs. The genes transcribed by RNA Pol III fall in the category of "housekeeping" genes whose ex ...

. They then undergo extensive post-transcriptional modifications, starting with the processing of the pri-miRNA in the nucleus to generate a 70-100 nt long pre-miRNA by ribonucleases

Drosha Drosha is a Class 2 ribonuclease III enzyme that in humans is encoded by the ''DROSHA'' (formerly ''RNASEN'') gene. It is the primary nuclease that executes the initiation step of miRNA processing in the nucleus. It works closely with DGCR8 and ...

and DGCR8. This pre-miRNA is then transported out of the nucleus by

Exportin-5 Exportin-5 (XPO5) is a protein that, in humans, is encoded by the ''XPO5'' gene. In Eukaryote, eukaryotic cells, the primary purpose of XPO5 is to export MicroRNA, pre-microRNA (also known as pre-miRNA) out of the Cell nucleus, nucleus and into the ...

, and is then further processed by

Dicer Dicer, also known as endoribonuclease Dicer or helicase with RNase motif, is an enzyme that in humans is encoded by the gene. Being part of the RNase III family, Dicer cleaves double-stranded RNA (dsRNA) and pre-microRNA (pre-miRNA) into shor ...

into a mature 18-25 nt long double stranded microRNA. The guide strand of the miRNA is then loaded into RNA-induced silencing complex (RISC) and is then able to pair with its target. The passenger strand, denoted by a star, is commonly degraded, though this is not always the case. MiR-203 is a microRNA that is specifically expressed in

keratinocyte Keratinocytes are the primary type of cell found in the epidermis, the outermost layer of the skin. In humans, they constitute 90% of epidermal skin cells. Basal cells in the basal layer (''stratum basale'') of the skin are sometimes referre ...

s (the most abundant cell type in the epidermis) and in normal conditions promotes epidermal differentiation by restricting proliferative potential and inducing cell-cycle exit. It does so by repressing p63, an essential regulator of

stem cell In multicellular organisms, stem cells are undifferentiated or partially differentiated cells that can change into various types of cells and proliferate indefinitely to produce more of the same stem cell. They are the earliest type of cell ...

maintenance in epithelial stratified tissues. Other proposed targets are suppressor of cytokine signaling 3 (SOCS3) and

ABL1 Tyrosine-protein kinase ABL1 also known as ABL1 is a protein that, in humans, is encoded by the ''ABL1'' gene (previous symbol ''ABL'') located on chromosome 9. c-Abl is sometimes used to refer to the version of the gene found within the mammali ...

. As is the case with many other microRNAs, miR-203 expression has been found dysregulated in several malignancies, including

rheumatoid arthritis Rheumatoid arthritis (RA) is a long-term autoimmune disorder that primarily affects synovial joint, joints. It typically results in warm, swollen, and painful joints. Pain and stiffness often worsen following rest. Most commonly, the wrist and h ...

and

carcinogenesis Carcinogenesis, also called oncogenesis or tumorigenesis, is the formation of a cancer, whereby normal cell (biology), cells are malignant transformation, transformed into cancer cells. The process is characterized by changes at the cellular, G ...

Localization

In mice, miR-203 is located in chromosome 12, within a fragile 7-Mb region that is lost is some hematopoietic malignancies. This region encodes 52 mature miRNAs, ~12% of the mammalian miRNA genome. In humans, this region is conserved and located intergenically in 14q32.

Tissue specificity

Sonkoly et al. found that miR-203 displays a highly organ- and tissue-specific expression across 21 human organs and tissues analyzed. miR-203 was expressed at highest level in skin and in the esophagus, an organ sharing anatomical similarities with skin. Yi et al. performed whole-mouse embryo in situ hybridization detecting miR-203-specific signal from the epidermis and the tongue. Skin-specific expression of miR-203 has been observed in zebrafish indicating that not only the sequence but the tissue specificity of miR-203 is preserved through evolution. Since these findings, the number of studies identified decreased miR-203 expression in various malignancies, mainly of epithelial origin.

Regulation

Regulation during differentiation

Sonkoly et al. demonstrated that expression of endogenous miR-203 expression is under the control of

protein kinase C In cell biology, protein kinase C, commonly abbreviated to PKC (EC 2.7.11.13), is a family of protein kinase enzymes that are involved in controlling the function of other proteins through the phosphorylation of hydroxyl groups of serine and t ...

pathway in epithelial cells. They demonstrated that

c-jun Transcription factor Jun is a protein that in humans is encoded by the ''JUN'' gene. c-Jun, in combination with protein c-Fos, forms the AP-1 early response transcription factor. It was first identified as the Fos-binding protein p39 and only l ...

suppresses, while another member of the AP-1 transcription factor complex, JUNB increases miR-203 expression. Growth factors, such as Epidermal growth factor can also suppress miR-203 in epithelial cells...

Regulation in tumors

Multiple mechanisms can suppress miR-203 expression in malignancies: Wellner et al. show that

ZEB1 Zinc finger E-box-binding homeobox 1 is a protein that in humans is encoded by the ''ZEB1'' gene. ZEB1 (previously known as TCF8) encodes a zinc finger and homeodomain transcription factor that represses T-lymphocyte-specific IL2 gene expression ...

represses expression of miR-203 together with the miR-200-family whose members are strong inducers of epithelial differentiation. They propose that ZEB1 links EMT-activation and stemness-maintenance by suppressing stemness-inhibiting microRNAs (miRNAs) and thereby is a promoter of mobile, migrating cancer stem cells. Sonkoly et al. demonstrated that activation of the

Hedgehog signaling pathway The Hedgehog signaling pathway is a signaling pathway that transmits information to embryonic cells required for proper cell differentiation. Different parts of the embryo have different concentrations of hedgehog signaling proteins. The pathwa ...

, can lead to decreased miR-203 expression in mouse model of basal cell carcinoma. They demonstrate that overexpression of

, a potent proto-oncogene commonly deregulated in a wide range of cancers suppresses miR-203 expression. Overexpression of

c-JUN Transcription factor Jun is a protein that in humans is encoded by the ''JUN'' gene. c-Jun, in combination with protein c-Fos, forms the AP-1 early response transcription factor. It was first identified as the Fos-binding protein p39 and only l ...

has been described in

basal cell carcinoma Basal-cell carcinoma (BCC), also known as basal-cell cancer, basalioma, or rodent ulcer, is the most common type of skin cancer. It often appears as a painless, raised area of skin, which may be shiny with Telangiectasia, small blood vessels ru ...

in which miR-203 is one of the most downregulated microRNA. McKenna et al. demonstrated that miR-203 expression in keratinocytes is dependent on regulation of p53 levels by E6, which may explain how expression of HPV16 E6 can disrupt the balance between proliferation and differentiation, as well as the response to DNA damage, in keratinocytes.

Evidence

This microRNA was predicted using computational tools by comparison to mouse and tiger blowfish sequences. It has been validated in zebrafish and its expression confirmed in humans by cloning and sequencing, where it was found in the outer layer of epidermis.

Targets

miR-203 has several validated targets. p63, conserved across vertebrate lineages. p63 is an essential regulator of stem cell maintenance in stratified epithelial tissues. Yi ''et al''. confirmed p63 as a target of miR-203. They showed that miR-203 expression is conspicuous in terminally differentiating epithelial cells, but is not present on their proliferative progenitor compartments, and shows a mutually exclusive pattern of expression with p63. They also report downregulation of proteins downstream of p63, suggesting a mechanistic method for inhibition of proliferative potential of epidermal stem cells. There is some controversy as to whether suppressor of cytokine signaling 3 (SOCS3) is also targeted by miR-203. In their study, Lena ''et al''. (2008) showed that, despite bioinformatic alignment of miR-203 with SOCS3 3'UTR, the levels of SOCS3 transcripts increased in keratinocytes stimulated to differentiate in vitro, in parallel with miR-203. Then they exogenously expressed miR-203 in mouse keratinocytes and showed that SOCS3 is not repressed by miR-203. In contrast, Wei ''et al''. (2010) validated SOCS3 as a target for miR-203. In their study, they introduced the SOCS3 3'UTR fragment encompassing the putative target site in a

luciferase Luciferase is a generic term for the class of oxidative enzymes that produce bioluminescence, and is usually distinguished from a photoprotein. The name was first used by Raphaël Dubois who invented the words ''luciferin'' and ''luciferase'' ...

reporter vector, and they observed a significant decrease in luciferase activity when miR-203 was introduced compared to controls. They also generated a mutation in the

binding site In biochemistry and molecular biology, a binding site is a region on a macromolecule such as a protein that binds to another molecule with specificity. The binding partner of the macromolecule is often referred to as a ligand. Ligands may includ ...

and reported restoration of luciferase activity, as well as mutually exclusive localization with miR-203. They concluded that SOCS3 is targeted by miR-203, and hypothesize that miR-203 regulation of SOCS3 and thus of

STAT3 Signal transducer and activator of transcription 3 (STAT3) is a transcription factor which in humans is encoded by the ''STAT3'' gene. It is a member of the STAT protein family. Function STAT3 is a member of the STAT protein family. In respon ...

could have implications in keratinocyte functions. Another validated target of miR-203 is

( AP-1), a potent proto-oncogene commonly deregulated in a wide range of cancers, including skin tumors. The suppression of miR-203 in BCC tumors was associated with a marked increase of c-JUN expression, evidenced by the intense and uniform distribution in BCC tumor nests. Similar to other miR-203 targets previously identified, such as p63, c-JUN was preferentially expressed in the basal, proliferative layer of healthy human epidermis. Another putative target is

, which is found activated in hematopoietic malignancies where miR-203 is

epigenetically In biology, epigenetics is the study of changes in gene expression that happen without changes to the DNA sequence. The Greek prefix ''epi-'' (ἐπι- "over, outside of, around") in ''epigenetics'' implies features that are "on top of" or "in ...

silenced by

hypermethylation Methylation, in the chemical sciences, is the addition of a methyl group on a substrate, or the substitution of an atom (or group) by a methyl group. Methylation is a form of alkylation, with a methyl group replacing a hydrogen atom. These terms ...

. In lung cancer cell lines, miR-203 has been shown to target

DKK1 Dickkopf-related protein 1 is a protein that in humans is encoded by the ''DKK1'' gene. Function This gene encodes a protein that is a member of the dickkopf family. It is a secreted protein with two cysteine rich regions and is involved in ...

, a secreted protein which acts as a survival factor in certain conditions. Its survival activity is only conditional because it requires the presence of its

transmembrane receptor Cell surface receptors (membrane receptors, transmembrane receptors) are receptor (biochemistry), receptors that are embedded in the cell membrane, plasma membrane of cell (biology), cells. They act in cell signaling by receiving (binding to) ex ...

protein KRM1. KRM1 is a Dependence Receptor and signals for

cell death Cell death is the event of a biological cell ceasing to carry out its functions. This may be the result of the natural process of old cells dying and being replaced by new ones, as in programmed cell death, or may result from factors such as di ...

until such signalling is blocked by binding of its survival factor ligand

. miR-203 mediated downregulation of DKK1 appears to make lung cancer cells easier to kill, suggesting that cancer cells upregulate DKK1 for their own survival and this protein would be a good target for downregulation in the treatment of such cancers. DKK1 is also a well known inhibitor of Wnt signalling and is required for the formation of head structures during embryonic development of most animals.

Foetal skin development

Yi ''et al''. showed that in mice, the expression of miR-203 is significantly upregulated between E13.5 and E15.5, suggesting that it may be absent from multipotent progenitors of single-layered epidermis, but is induced upon stratification and differentiation. It also was expressed at high levels in differentiating cells such as hair follicles, epidermis and sebaceous glands. Wei ''et al''. demonstrated that in humans, miR-203 expression is first detectable at 17 weeks

gestation Gestation is the period of development during the carrying of an embryo, and later fetus, inside viviparous animals (the embryo develops within the parent). It is typical for mammals, but also occurs for some non-mammals. Mammals during pregn ...

in the suprabasal layers of epidermis, and this localization was conserved in the adult skin. When miR-203 is expressed prematurely, basal cells diminish their proliferative potential; and when it is absent, proliferation is no longer restricted to the basal layer of epidermis.

Role in carcinogenesis

miR-203 has been found overexpressed in pancreatic adenocarcinoma and shows correlation with poor

prognosis Prognosis ( Greek: πρόγνωσις "fore-knowing, foreseeing"; : prognoses) is a medical term for predicting the likelihood or expected development of a disease, including whether the signs and symptoms will improve or worsen (and how quickly) ...

in patients that had undergone

pancreatectomy In medicine, a pancreatectomy is the surgical removal of all or part of the pancreas. Several types of pancreatectomies exist, including pancreaticoduodenectomy (Whipple procedure), distal pancreatectomy, segmental pancreatectomy, and total pancr ...

, and has been suggested as a new prognostic marker for this disease. Also, miR-203 has been identified as target of human papillomavirus (HPV) protein E7, which causes its downregulation and thus de-repression of p63 and its downstream targets, ensuring proliferative potential on the host cell, required for the virus to replicate. High levels of miR-203 are inhibitory of HPV amplification. miR-203 has also been proposed as a tumour-suppressive microRNA in

hepatocellular carcinoma Hepatocellular carcinoma (HCC) is the most common type of primary liver cancer in adults and is currently the most common cause of death in people with cirrhosis. HCC is the third leading cause of cancer-related deaths worldwide. HCC most common ...

(HCC) and hematopoietic malignancies. In their study, Furuta ''et al''. found miR-203, along with miR-124, epigenetically silenced in primary HCC tumours compared with non-tumorous liver tissues. Also, expression of miR-203 in HCC cells lacking their expression inhibited cell growth and downregulated a set of other possible targets. Bueno ''et al''. also found silencing of miR-203 in some leukemias, as well as an inverse correlation between miR-203 and ABL1 levels (sometimes expressed as the BCR-ABL1 fusion protein). Supporting its role as a tumour suppressor, it has also been found upregulated upon UVC irradiation in the

squamous cell carcinoma Squamous-cell carcinoma (SCC), also known as epidermoid carcinoma, comprises a number of different types of cancer that begin in squamous cells. These cells form on the surface of the skin, on the lining of hollow organs in the body, and on the ...

lines, suggesting a connection between miR-203 and the activation of the apoptotic program. miR-203 acts as a tumor suppressor in basal cell carcinoma (BCC) in which it forms a double-negative feedback-loop with its verified target

(AP1). This regulatory circuit provides functional control over basal cell proliferation and differentiation. Its expression was suppressed in K5TreGli1 trangenic mice, due to activated Hedgehog signaling. Further supporting the role of miR-203 as a tumor suppressor, in vivo delivery of miR-203 mimics in a BCC mouse model results in the reduction of tumor growth.

Role in psoriasis and rheumatoid arthritis

Sonkoly ''et al''. identified miR-203, along with miR-146a, miR-21, and miR-125b; as a psoriasis-specific microRNA when compared with healthy human skin or atopic eczema. They also observed downregulation of SOCS3 concurrently with upregulation of miR-203 in psoriatic plaques, potentially having an effect in inflammatory responses. Stanczyk ''et al''. found overexpression of miR-203 in rheumatoid arthritis synovial fibroblasts (RASFs) compared to healthy or osteoarthritis samples; and inforced expression of miR-203 led to higher levels of MMP-1 and IL-6 and thus contributed to the activated phenotype of RASFs. MiR-203 regulation was found to be methylation-dependent.