SRC ACTIVATES TROP2 VIA CYCLIN D1

Proteomic analysis of castration-resistant prostate cancer demonstrated the enrichment of SRC tyrosine kinase activity in approximately ninety percent of patients. Src is known to induce cyclin D1, and a cyclin D1-regulated gene expression module predict poor outcome in human prostate cancer. The tumor-associated calcium signal transducer 2 [TACSTD2/Trop2/M1S1] is enriched in the prostate, promoting prostate stem cell self-renewal upon proteolytic activation via a γ-secretase cleavage complex (PS1, PS2) and TACE (ADAM17), which releases the Trop2 intracellular domain (Trop2 ICD). Herein, v-Src transformation of primary murine prostate epithelial cells increased the proportion of prostate cancer stem cells as characterized by gene expression, epitope characteristics and prostatosphere formation. Cyclin D1 was induced by v-Src, and Src kinase induction of Trop2 ICD nuclear accumulation, required cyclin D1. Cyclin D1 induced abundance of the Trop2 proteolytic cleavage activation components (PS2, TACE) and restrained expression of the inhibitory component of the Trop2 proteolytic complex (Numb). Prostate cancer patients with increased nuclear Trop2 ICD and cyclin D1, and reduced Numb, had reduced recurrence-free survival probability (hazard ratio 4.35). Cyclin D1 therefore serves as a transducer of v-Src-mediated induction of Trop2 ICD by enhancing abundance of the Trop2 proteolytic activation complex.

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