198 IN HEALTH AND DISEASE Shailja Chatterjee Assistant Professor, Department of Oral and Maxillofacial and Microbiology, MMCDSR, M. M. University, Mullana (Ambala), Haryana-133203.

Corresponding Author: Shailja Chatterjee, Department of Oral and Maxillofacial Pathology and Microbiology, MMCDSR, M.M.University, Mullana(Ambala), Haryana-133203, Email: [email protected], Ph: 08053047175

Abstract Objective: Cytokeratins are -specific intermediate filaments. Their altered expression is evident in various benign, hyperplastic and neoplastic lesions. This review provides an in-depth description of expression patterns in odontogenesis; normal development, hyperplastic/benign and malignant lesions or conditions. Materials and methods: Cytokeratin expression can be studied by numerous techniques like , immunofluorescence and in situ hybridization. Results: The variable expressivity of cytokeratins is a subject of continuous deliberation and ongoing research. This paper gives an in-depth analysis of cytokeratin expression in a variety of epithelial tissues. Conclusion: Cytokeratins are universal indicators of epithelium specificity. An alteration of expression can be well understood by means of a proper understanding of their normal presence. Key words: Cytokeratin, benign, malignant, odontogenesis, development.

Introduction Cytokeratin pattern complexity shows great Cytokeratins are epithelium-specific variation in expression in tumors. Epithelium- intermediate filaments with diameters derived tumors maintain the expression of measuring between 6 nm () to 25 many cytokeratin polypeptides characteristic of nm (). All human epithelial nontransformed cells. However, certain are defined by “Co-expression”. It is cytokeratins are not expressed at the same time. the existence of keratins in pairs of which, one This can be attributed to selection process is acidic (type I; CK 1 to 8) and other, basic (type during transformation and tumor II; CK 9 to 20). This division is based upon development from a cell type that is not properties of charges, immunoreactivities, quantitatively predominant in total tissue used mRNA hybridization, peptide-mapping for comparison. Thus, explaining the patterns, sequences and relationship predominance of a particular cytokeratin in a to keratin1. tumor. Cytokeratin expression in normal oral pairs exhibit specificity with mucosa each pair comprising of a basic and an acidic 2 A. Cytokeratins 5 and 14 (CK5/14): This member . For example, CK1 and CK10 are found mainly in keratinized epithelia. Keratins cytokeratin pair is strongly expressed are markers of differentiation rather than consistently in the basal cell layer of both lineages. In stratified squamous epithelium, keratinized and nonkeratinized mucosae. Its differentiating epithelial cells synthesize a expression decreases towards the upper cell 3 sequence of different keratins as they migrate layers i.e., . towards the upper cell layers. This is evident B. Cytokeratin 1 and 10 (CK 1/10): CK 1 from the expression of CKs 5 and 14 in the and 10 are early markers of keratin basal layer of both the keratinized and non- differentiation. They are strongly expressed keratinized stratified squamous epithelia. The in stratum spinosum which forms the first differentiating upper layers contain the keratin layer of differentiation compartment. Their pairs, CK1/10 (keratinized) and CK4/13 expressivity declines in stratum granulosum (nonkeratinized). Oral & Maxillofacial Pathology Journal [ OMPJ ] Vol. 3 No. 1 Jan - June -2012 ISSN 0976 - 1225 Cytokeratins In Health And Disease 199 and upper cell layers. This cytokeratin pair is enamel epithelium expresses CK7, CK14 and absent in parabasal cell layer. However, its CK19. The cells of dental lamina remnants are presence is detectable as mRNAs i.e., it is immunopositive for CK7; with sporadic CK 13 expression. However, CK14 is the most strongly regulated at post-transcriptional level as 7 labeled cytokeratin in these cells . evident by its strong expression in parabasal cells in pathologically altered mucosa. It is Cytokeratin expression patterns in expressed strongly in hard palate, fungiform pathological states papillae and labial i.e., I. Squamous cell : orthokeratinized epithelia4,5. A. CK19 (CYFRA 21.1): Cyfra 21.1 is a C. Cytokeratin 19: It is found in a wide solubilized fragment of cytokeratin 19 range of epithelial tissues and appears generated by necrosis of tumor cells. It is usually as a major component in simple found in serum and shows 50% to 60% 8 epithelia and a minor component in sensitivity in head and neck SCC . CK19 stratified squamous epithelium as well as expression is normally seen in basal cells of cultured . Expressed in basal nonkeratinized epithelium and is cell layer of nonkeratinized mucosa with considered to be a marker of premalignancy variable suprabasal expression and when appearing in suprabasal cells. sometimes, full thickness of B. K13/14/5: Reduced expression of CK13 nonkeratinizing epithelia3. and suprabasal CK14 (which is ubiquitous) D. Cytokeratins 4 and 13 (CK4/13): This is seen along with expression in infiltrating cytokeratin pair forms a component of tumor islands. CK5 is not expressed with nonkeratinized stratified squamous increasing grades of dysplasia. The expression of CK 5 is thus, an early event in epithelium and is associated with 9 differentiating suprabasal cells. For example, tobacco-associated pathological changes . mucosa (anterior compartment) and C. Well and moderately differentiated SCCs: In buccal mucosa3. well-differentiated SCCs, CK4 and 13 are co-expressed with CK1/10 in the same E. K2p: Suprabasal epithelial cells of the group of cells, including the cells at hard palate and gingiva express K2p. periphery of tumor islands. Moderately- Cytokeratin expression in odontogenesis differentiated SCCs show a substitution of Odontog enesis is a complex CK4/13 by CK1/104,5. embryological process characterized by D. Poorly differentiated SCCs: In poorly reciprocal epithelial-mesenchymal interactions, differentiated SCCs, differentiation keratins culminating in differentiation. The are absent. This can be attributed to the epithelial cells of human dental lamina and impaired epithelial maturation or loss of enamel organ express CKs 7, 13, 14 and 19 with pattern of keratin expression4,5. slight changes in pattern during the E. CK18: Aberrantly expressed in normal oral differentiation phases of odontogenesis. tissues, without good hygiene status. CK14 is strongly expressed in inner epithelial Therefore, it is indicative of initiation of cells at early bell stage, but is downregulated and 10 replaced by CK19 at late bell stage when abnormal cell differentiation . complete differentiation of ameloblasts has taken place. CK14 has a binding affinity with II. Disease progression from oral submucous amelogenin. The CK 14 molecule acts as a fibrosis to oral cancer: Higher molecular chaperon for nascent amelogenic polypeptide weight cytokeratins (CK1/10 and CK5/14) during amelogenesis6. show an increase in staining intensity in The stellate reticulum stains for CK7 at OSMF and OSCC. Pancytokeratin cocktail early bell stages along with CK14 which is comprising of CK1/10; 4/13; 5/14; 6/16; 1 strongly present at early bell stage. The outer 7/19; 2/3; 8/15, also show a significant . Oral & Maxillofacial Pathology Journal [ OMPJ ] Vol. 3 No. 1 Jan - June -2012 ISSN 0976 - 1225 Cytokeratins In Health And Disease 200 increase in staining intensity from normal tissue D. CK7: It shows negative expression in to OSMF to OSCC11. radicular cysts. Only superficial layers are positive in dentigerous cysts. III. Epithelial dysplasia: The variable E. CK10: It is more significantly expressed in expression of differentiation keratins in Odontogenic keratocysts as compared to mild and moderate oral epithelial dysplasia other odontogenic cysts. is partly dependent on altered epithelial F. CK13: It is expressed in suprabasal cell differentiation. Disturbed differentiation is layers of all odontogenic cysts. a major feature of dysplasia. In mild lesions G. CK20: All odontogenic cysts are negative. derived from non-keratinized epithelium, K1/10 synthesis is enhanced and K4/13 is V. Odontogenic tumors: retained. This can be explained by the i. Ameloblastoma: presence of K1/10 mRNAs, synthesis of a. Follicular Ameloblastoma: The central which is increased in dysplastic state9. stellate reticulum-like cells and basal ends In moderate dysplasia arising from non- of columnar cells stain with wide- keratinizing epithelia, K1/10 filaments spectrum keratins. Central stellate cells of completely replace the K4/13 complex. In follicular ameloblastoma show a high severe dysplasia, both K4/13 and K1/10 frequency of high molecular weight complete are absent. CK5/14 keratins that cytokeratins than Plexiform type, are normally expressed in basal cells, are therefore, indicating presence of elements also expressed in parabasal and spinous cell 13 of squamous differentiation . layers in dysplastic epithelia. This b. Acanthomatous Ameloblastoma: expression pattern probably reflects upon the basilar hyperplasia in dysplastic Expression is same as above. epithelium. Furthermore, the keratins c. Basal cell Ameloblastoma: Cells are (K4/13 or K1/10) that are characteristically partly stained with wide-spectrum keratins. present in suprabasal cell layers show d. Plexiform Ameloblastoma: Cells are reduced expression or loss in epithelial stained with wide-spectrum or HMW dysplasia. Thus, in severe dysplasia, K4/13 cytokeratins. is completely lost. In normal epithelium, ii. SquamousOdontogenic tumor: Polyclonal keratins 8 and 18 are present as mRNA are expressed in entire epithelial transcripts in basal and lower spinous cell strata. CK1 is expressed in upper spinous layers. However, in oral epithelial dysplasias, and granular layer cells, whereas, LMW these keratins are detectable by routine IHC keratin expression is confined to basal cell 9 i n m o s t o f t h e c a s e s . C K 1 9 layer14. immunopositivity is found in basal and a. Calcifying Epithelial Odontogenic Tumor: parabasal cell layers in moderately to The tumor cells of CEOT are severely dysplastic epithelia. morphologically similar to the stratum IV. Odontogenic cysts intermedium cells and are also positive for (OKCs/Dentigerous/Radicular cysts)12: alkaline phosphatases and adenosine A. CK19: It is completely absent in triphosphate. They are strongly positive for Odontogenic keratocysts. Positive 15 cytokeratins (CK1, 5, 6, 8, 13 and 16) . expression is seen in dentigerous and iii. Calcifying cystic odontogenic tumor: The radicular cysts. basal cell layers express CK14, whereas, the B. CK17: Majority of OKCs are upper cell layers express CK10/13. immunopositive for CK17 and negative for CK10/13 expression is seen in squamous dentigerous and radicular cysts. and stellate reticulum-type tumoral cells C. CK5/6: It is expressed in all three identifying with similarity in expression in Odontogenic cysts in all cell layers. upper layers of squamous-type reduced in Oral & Maxillofacial Pathology Journal [ OMPJ ] Vol. 3 No. 1 Jan - June -2012 ISSN 0976 - 1225 Cytokeratins In Health And Disease 201 enamel epithelium and some dental lamina cells. VIII. Salivary gland neoplasms: CK19 is expressed in the basal cell layer of Role of cytokeratin 5 in development of salivary COC which is similar to . gland Therefore, it can be hypothesized that The inducible expression of a mutated K- CCOT epithelium differentiates towards ras under the influence of CK5 promoter stratified squamous type and has an leads to the development of hyperplastic apparent relationship to reduced enamel and dysplastic epithelial lesions and epithelium. These CK10/13 positive cells carcinomas. These tumors appear to arise are the squamous transitory elements from CK 5 positive basal cell compartment. towards ghost cell development and are Thus, the ras oncogene when targeted to a placed towards the plasma membrane. specifically sensitive cell compartment These cells accumulate certain other within the salivary glands can trigger a series substance during the differentiation of events that are sufficient for causing process, and gradually repel the cytoskeletal carcinogenesis23. system to the periphery, until becoming CK10/13 negative ghost cells16. IX. Keratin2e: K2e expression in is resultant of keratinocytes activation, VI. Cell Rests of Malassez and periapical however, it is up-regulated in oral lesions as lesions17: a reflection of degree of ortho i. CKs4/13: These are not expressed in cell keratinization. For example, benign rests but in altered epithelium of periapical keratoses of lingual mucosa where it is with increasing intensity of coexpressed with CK1 and CK10. In mild expression with transition to periapical t o m o d e r a t e d y s p l a s i a w i t h cysts. orthokeratinization, it is highly expressed ii. CK19: CK19 is coexpressed with CK5 in compared with parakeratinized as mRNA cell rests of various odontogenic epithelia. transcripts4,5. In proliferated epithelia, CK19 expression is Conclusion suprabasal and in cyst lining, often restricted Cytokeratins are an important tool in to most superficial cell layers. molecular progression of certain diseases, their embryological development and lineage. Use of VII. Salivary gland morphogenesis: Numerous techniques like immunohistochemistry and studies have indicated that cytokeratins can polymerase chain reaction, aid in establishing serve as the most useful marker in epithelial the true nature and diagnosis of lesions with morphogenesis in a variety of systems including suspected nature. Thus, an in-depth knowledge salivary glands. 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