CK5 (Cytokeratin 5) is a member of the keratin family, intermediate filament proteins critical for maintaining structural integrity in epithelial cells. Expressed primarily in basal epithelial cells, CK5 pairs with CK14 to form heterodimers, contributing to cell adhesion, mechanical stability, and signaling. It is a marker of progenitor or stem cells in stratified epithelia, such as skin, mammary glands, and the respiratory tract.
In pathology, CK5 antibodies are widely used as diagnostic tools. CK5 expression helps classify epithelial tumors, particularly breast cancers. Basal-like breast carcinomas, which are often triple-negative (ER-/PR-/HER2-), typically show CK5 positivity, aiding in subtype identification and prognosis assessment. CK5 is also co-expressed with CK6 in hyperproliferative skin disorders (e.g., psoriasis) and squamous cell carcinomas.
Research applications include studying epithelial differentiation, wound healing, and cancer stem cell behavior. Commercially available monoclonal antibodies target specific CK5 epitopes for immunohistochemistry (IHC) or immunofluorescence. However, cross-reactivity with other keratins (e.g., CK6) requires careful validation. Its role in tumor invasiveness and resistance mechanisms remains an active research area, highlighting CK5's clinical and biological relevance.