Ack1: Activation and Consequences in Prostate Cancer

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DESCRIPTION (provided by applicant): Prostate cancer, the most common male malignancy, takes the lives of 30,000 men annually, as it progresses to a hormone-refractory cancer that invades surrounding tissue and bone. Our investigation into prostate cancer cell tyrosine kinase signaling revealed that Ack1, an under-studied, intracellular tyrosine kinase, never before suggested as a prostate cancer oncogene, may in fact have a profound effect on prostate cancer progression to androgen independence. Ack1 is found activated in advanced human prostate tumors; moreover, active Ack1 converts the poorly tumorigenic, androgen-dependent LNCaP cells into a rapidly- growing, invasive, androgen-independent tumor in immunodeficient mice. We identified Ack1 by mass spectroscopic protein sequencing as a downstream target of the Mer receptor tyrosine kinase in prostate cells. LNCaP cells, stably transfected with active Ack1 (as compared to vector control or kinase dead Ack1), demonstrated minimally increased growth in culture, substantially increased soft agar growth and, as noted, remarkably accelerated tumorigenesis in nude mice, even when castrated prior to tumor implantation. We have shown that Ack1 directly tyrosine phosphorylates the androgen receptor (AR), resulting in ligand-independent AR activity. Examination of human prostate cancer biopsy specimens revealed tyrosine phosphorylated (auto-activated) Ack1 and tyrosine phosphorylated AR protein in ~44 % of androgen- independent prostate cancer specimens, but not in androgen-dependent or benign prostate. We provide evidence that active Ack1 has at least three functions: i) growth stimulation, presumably in part through AR- dependent mechanism, ii) sending a survival signal that is not dependent on the AR, and iii) stimulating invasion in collagen matrix and in nude mouse models. We have created a novel transgenic mouse model of Ack1-driven prostate neoplasia and preliminary studies indicate that prostate-specific expression of active Ack1 induces progressive prostate pathology from hyperplasia to prostate intraepithelial neoplasia to adenocarcinoma of the prostate. Our objectives are to: i) develop transgenic mouse models in which to study the effects of persistent Ack1 activity in the prostate epithelium, enabling the genetic analysis of the role of Ack1 in prostate neoplasia and ii) elucidate the signaling pathways altered by Ack1 activity that contribute to increased growth, survival, invasiveness and androgen-independence. Aim 1 is to determine whether prostate-specific expression of an activated Ack1 transgene accelerates tumorigenesis, invasion or metastasis in the mouse - by itself or in combination with genetically engineered mouse models of prostate neoplasia. Aim 2 is to determine the role of androgen receptor phosphorylation in Ack1-driven prostate carcinogenesis using a mouse knock-in model. Aim 3 is to characterize the in vivo tumorigenic properties (metastasis, bony invasion, etc.) of Ack1 accelerated prostate cancer growth, define their mechanism, and validate their involvement in tumor growth. Our data establish a novel mechanism of prostate tumor development and progression that is observed in an active state in human prostate cancer specimens. Our proposed work will establish its mechanism of action and activation, and thus provide new targets for treatment of advanced prostate cancer. PUBLIC HEALTH RELEVANCE: Although androgen deprivation therapy has been the mainstay of treatment for metastatic prostate cancer for over 60 years, inevitable progression to the terminal stage with no effective treatment makes development of new therapeutic options for prostate cancer an urgent priority. Ack1 tyrosine kinase appears to play a critical role in prostate cancer progression. This proposal has the potential to yield significant new information about how Ack1 promotes prostate cancer progression and may lead to novel ways of treating prostate cancer patients by targeting Ack1 tyrosine kinase with new drugs.