Crocin Suppresses Constitutively Active STAT3 Through Induction of Protein Tyrosine Phosphatase SHP-1: CROCIN SUPPRESSES CONSTITUTIVELY ACTIVE STAT3 IN U266 CELLS

: The aim of the present study is to investigate the effect of a natural compound crocin, one of the active components of saffron, on human multiple myeloma cells. Crocin effectively suppressed constitutive STAT3 activation, translocation of STAT3 to the nucleus, and its target gene expression. The suppression of STAT3 was mediated through the inhibition of activation of protein tyrosine kinases JAK1, JAK2, and c-Src. We found that crocin induced the expression of SHP-1, a tyrosine protein phosphatase, and pervanadate treatment reversed the crocin-induced downregulation of STAT3, suggesting the involvement of a protein tyrosine phosphatase. Moreover, suppression of SHP-1 by its inhibitor overturned the effect of crocin on induction of SHP-1 and the inhibition of STAT3 activation. Finally, crocin downregulated the expression of STAT3-mediated gene products including anti-apoptotic (Bcl-2), pro-apoptotic (BAX), invasive (CXCR4), angiogenic (VEGF), and cell cycle regulator (cyclin D1), which are correlated with suppression of proliferation, the accumulation of cells in sub-G1 phase of cell cycle, and induction of apoptosis. Overall, our results suggested that crocin is a novel inhibitor of STAT3 activation pathway and thus may have potential in prevention and treatment of human multiple myeloma. J. Cell. Biochem. 118: 3290-3298, 2017. © 2017 Wiley Periodicals, Inc.