Mesenchymal splice isoform of CD44 (CD44s) promotes EMT/invasion and imparts stem-like properties to ovarian cancer cells.

Increased metastasis and a precipitous recurrence contribute to the lethality of ovarian cancer (OC). Several molecular mechanisms including aberrant-splicing have been closely associated with the extent of cancer progression. Numerous gene transcripts are differentially spliced in cancer cells, CD44 being one of them. CD44 splice isoforms contribute to the aggressiveness and gain of stem-like properties in different cancer types, but their role in ovarian cancer remains to be elucidated. We observed augmented CD44 levels in human ovarian cancer patient samples correlated with enhanced expression of the mesenchymal spliced variant CD44s (standard) and a concurrent decrease in the epithelial variants (CD44v). Moreover, CD44s was upregulated upon TGFβ1-induced EMT, which was mediated through the downregulation of the splicing factor, ESRP1. Furthermore, overexpression of this mesenchymal isoform in the OC cells induced EMT and invasion, followed by the gain of stem-like characteristics and chemoresistance. Since all these phenomena render lethality to this disease type, CD44s can be attributed for playing a major role in deregulated-splicing mediated ovarian cancer progression.