Srcasm overexpression in psoriasis-insights into pathogenesis

Tyrosine kinases in inflammatory dermatologic disease

Tyrosine kinases (TKs) are enzymes that catalyze the phosphorylation of tyrosine residues on protein substrates. They are key components of signaling pathways that drive an array of cellular responses including proliferation, differentiation, migration, and survival. Specific TKs have recently been identified as critical to the pathogenesis of several autoimmune and inflammatory diseases. Small-molecule inhibitors of TKs are emerging as a novel class of therapy that may provide benefit in certain patient subsets. In this review, we highlight TK signaling implicated in inflammatory dermatologic diseases, evaluate strategies aimed at inhibiting these aberrant signaling pathways, and discuss prospects for future drug development.

Decreased Srcasm expression in hyperproliferative cutaneous lesions

BACKGROUND

Src-family tyrosine kinases (SFKs) are signaling proteins that regulate keratinocyte proliferation and differentiation. Src-activating and signaling molecule (Srcasm) is a recently identified molecule that downregulates SFK activity and promotes keratinocyte differentiation. To determine if Srcasm expression correlates with keratinocyte differentiation, we characterized the level of Srcasm expression in some cutaneous lesions that exhibit increased keratinocyte proliferation.

METHODS

Formalin-fixed sections of randomly selected seborrheic keratoses (SKs) and basal cell carcinomas (BCCs) were analyzed for Srcasm and Ki-67 immunohistochemical staining. Anti-Srcasm and anti-Ki-67 stainings were performed in parallel.

RESULTS

All SKs displayed decreased Srcasm staining in areas comprised of basaloid keratinocytes that exhibited an increased Ki-67 index. Higher Srcasm staining levels were detected near pseudohorn cysts where keratinocytes exhibited a lower Ki-67 index. All multicentric and nodular BCCs displayed a prominent loss of Srcasm staining in association with a marked increase in Ki-67 staining.

CONCLUSIONS

Our results support the hypothesis that Srcasm protein levels are decreased in the hyperproliferative keratinocytes found in SKs and BCCs. Increased Srcasm protein levels are detected in keratinocytes undergoing differentiation. Decreased Srcasm levels may be part of the pathophysiologic mechanism in cutaneous lesions, exhibiting keratinocyte hyperproliferation.