Activated Tyrosine Kinase Ack1 Promotes Prostate Tumorigenesis: Role of Ack1 in Polyubiquitination of Tumor Suppressor Wwox

Abstract

Aberrant activation of tyrosine kinases is linked causally to human cancers. Activated Cdc42-associated kinase (Ack1), an intracellular tyrosine kinase, has primarily been studied for its signaling properties but has not been linked to specific pathologic conditions. Herein, we report that expression of activated Ack1 in LNCaP cells, while minimally increasing growth in culture, enhanced anchorage-independent growth in vitro and dramatically accelerated tumorigenesis in nude mice. Molecular chaperone heat shock protein 90B (Hsp90B)-bound Ack1 and treatment of cells with geldanamycin, a Hsp90 inhibitor, inhibited Ack1 kinase activity and suppressed tumorigenesis. Further, we identify the tumor suppressor WW domain containing oxidoreductase (Wwox) as an Ack1-interacting protein. Activated Ack1 tyrosine phosphorylated Wwox, leading to rapid dissociation of the Ack1-Wwox complex and concomitant Wwox polyubiquitination followed by degradation. Tyrosine phosphorylation of Wwox was critical for its degradation, as splice variant Wwox#5-8 that was not phosphorylated by Ack1 failed to undergo polyubiquitination and degradation. It has been reported that phosphorylation of Wwox at Tyr 33 stimulated its proapoptotic activity. We observed that Y33F Wwox mutant was still tyrosine phosphorylated and polyubiquitinated by Ack1 action. Site-directed mutagenesis revealed that activated Ack1 primarily phosphorylated Wwox at Tyr 287 , suggesting that phosphorylation of distinct tyrosine residues activate or degrade Wwox. Primary androgen-independent prostate tumors but not benign prostate showed increased tyrosinephosphorylated Ack1 and decreased Wwox. Taken together, these data indicate that Ack1 stimulated prostate tumorigenesis in part by negatively regulating the proapoptotic tumor suppressor, Wwox. Further, these findings suggest that Ack1 could be a novel therapeutic target for prostate cancer. (Cancer Res 2005; 65(22): 10514-23)

Cancer-associated Mutations Activate the Nonreceptor Tyrosine Kinase Ack1

“…Ack1 has previously been implicated in tumorigenesis (11,12), cell survival (10), and metastasis (9). The Ack1 gene is amplified and overexpressed in a number of tumors, and the copy number change correlates with later stage, more aggressive tumors (9).…”

“…In v-Ras-transformed mammalian cells, Ack1 is required for the maintenance of the transformed phenotype (10). Ack1 contributes to prostate tumorigenesis by phosphorylating the tumor suppressor protein Wwox, leading to its degradation (11), and by phosphorylating androgen receptor (12).…”

Molecular alterations in the tumor suppressor gene WWOX in oral leukoplakias

“…34,35 WWOX gene underexpression in human cancers could result from distinct events such as allelic losses, point mutations, promoter hypermethylation, aberrant mRNA transcription, or a combination of two or more events resulting in a loss of tumor suppressor activity. 36 Point mutations are rare in WWOX gene 28 but loss of heterozygosity of WWOX allele is observed in a variety of cancers. 15,28,37 The expression of some tumor suppressor genes is downregulated in many cancers by epigenetic mechanisms.…”

“…Furthermore, two lesions with reduced protein expression (#OL4 and #OL6) did not exhibit any abnormality at genetic level, thus the possibility of WWOX hypermethylation or deletion of one allele cannot also be excluded. 36,39 In addition, despite we have performed microdissection, the possibility of contamination with non-epithelial cells should not be discarded.…”

A High Precision Survey of the Molecular Dynamics of Mammalian Clathrin-Mediated Endocytosis

“…The recruitment signature of GAK defined a module including ACK1, a serine threonine kinase implicated in tumorigenesis [58] and OCRL1, a 59 phosphatase and Rab5a effector [59]. Interestingly, GAK and OCRL1 were recruited only after scission, whereas ACK1 was gradually recruited as CCSs matured ( Figure 4A).…”