Dasatinib inhibits site-specific tyrosine phosphorylation of androgen receptor by Ack1 and Src kinases

UNC Lineberger Comprehensive Cancer Center, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599-7295, USA.
Oncogene (Impact Factor: 8.46). 04/2010; 29(22):3208-16. DOI: 10.1038/onc.2010.103
Source: PubMed


Activation of androgen receptor (AR) may have a role in the development of castration-resistant prostate cancer. Two intracellular tyrosine kinases, Ack1 (activated cdc42-associated kinase) and Src, phosphorylate and enhance AR activity and promote prostate xenograft tumor growth in castrated animals. However, the upstream signals that activate these kinases and lead to AR activation are incompletely characterized. In this study, we investigated AR phosphorylation in response to non-androgen ligand stimulation using phospho-specific antibodies. Treatment of LNCaP and LAPC-4 cells with epidermal growth factor (EGF), heregulin, Gas6 (ligand binding to the Mer receptor tyrosine kinase and activating Ack1 downstream), interleukin (IL)-6 or bombesin stimulated cell proliferation in the absence of androgen. Treatment of LNCaP and LAPC-4 cells with EGF, heregulin or Gas6 induced AR phosphorylation at Tyr-267, whereas IL-6 or bombesin treatment did not. AR phosphorylation at Tyr-534 was induced by treatment with EGF, IL-6 or bombesin, but not by heregulin or Gas6. Small interfering RNA-mediated knockdown of Ack1 or Src showed that Ack1 mediates heregulin- and Gas6-induced AR Tyr-267 phosphorylation, whereas Src mediates Tyr-534 phosphorylation induced by EGF, IL-6 and bombesin. Dasatinib, a Src inhibitor, blocked EGF-induced Tyr-534 phosphorylation. In addition, we showed that dasatinib also inhibited Ack1 kinase. Dasatinib inhibited heregulin-induced Ack1 kinase activity and AR Tyr-267 phosphorylation. In addition, dasatinib inhibited heregulin-induced AR-dependent reporter activity. Dasatinib also inhibited heregulin-induced expression of endogenous AR target genes. Dasatinib inhibited Ack1-dependent colony formation and prostate xenograft tumor growth in castrated mice. Interestingly, Ack1 or Src knockdown or dasatinib did not inhibit EGF-induced AR Tyr-267 phosphorylation or EGF-stimulated AR activity, suggesting the existence of an additional tyrosine kinase that phosphorylates AR at Tyr-267. These data suggest that specific tyrosine kinases phosphorylate AR at distinct sites and that dasatinib may exert antitumor activity in prostate cancer through inhibition of Ack1.

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    • "A correlation has been demonstrated between AR expression or activity and Src activation in PCa (8, 21, 90). The tyrosine Y534 in the AR would be the Src target (17, 19, 21, 91) and its phosphorylation would result in ligand-independent AR activation, which is an important mechanism to explain resistance to castration. Activated Src would also inhibit AR interaction with co-repressors, thereby increasing its capacity to be activated without ligand binding (92). "
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    • "This correlates with increased activation levels on non-receptor tyrosine kinases 32 as well as receptor tyrosine kinases such as Met 33, c-Kit 34 and the EGFR family 35, 36. However, the role of AR tyrosine phosphorylation may have been underappreciated because it is not induced by androgens such as dihydrotestosterone (DHT), whereas it is induced by EGF, heregulin, IL-6 or serum 20, 37, 38. In contrast, androgens induce IGF-1R activity in prostate cancer progression 39. "
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