Phosphorylation of ErbB4 on Tyr1056 is critical for inhibition of colony formation by prostate tumor cell lines

Abstract

Correspondence to: David J. Riese II, Purdue Cancer Research Center, 201 S. University Street, West Lafayette, Indiana, 47907-2064, Tel (765) FAX (765) We have previously demonstrated that the constitutively-active Q646C mutant of the ErbB4 receptor tyrosine kinase inhibits colony formation by human prostate tumor cell lines. Here we use ErbB4 mutants to identify ErbB4 functions critical for inhibiting colony formation. A derivative of ErbB4 Q646 that lacks kinase activity fails to inhibit colony formation by prostate tumor cells. Likewise, an ErbB4 Q646C mutant in the context of the CT-b splicing isoform fails to inhibit colony formation. Mutation of tyrosine 1056 to phenylalanine abrogates inhibition of colony formation whereas an ErbB4 mutant that lacks all of the putative sites of tyrosine phosphorylation except for tyrosine 1056 still inhibits colony formation. Given that tyrosine 1056 is missing in the CT-b isoform, these results suggest that phosphorylation of tyrosine 1056 is critical for function. Indeed, an ErbB4 mutant that lacks kinase activity but has a glutamate phosphomimic residue substituted for tyrosine 1056 inhibits colony formation. Finally, one-dimensional phosphopeptide mapping indicates that ErbB4 Q646C is phosphorylated on tyrosine 1056. These data suggest that phosphorylation of ErbB4 tyrosine 1056 is critical for coupling ErbB4 to prostate tumor suppression.

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“…In control tumors, ErbB2 was phosphorylated at tyrosine 1221/1222 and is associated with high tumor grade and with shorter disease-free survival and overall survival (Frogne et al, 2009). Similarly, ErbB4 is able to induce phosphorylation of phosphatidylinositol 3-kinase regulatory subunit which is a pro-survival protein that prevents apoptosis (B. D. Gallo et al, 2006). Our data suggests that dephosphorylation of ErbB4 tyrosine 1284 is critical for tumor regression in the dual treatment group.…”

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“…Moreover, ErbB4 expression in breast tumor samples correlates with a more favorable prognosis (Kew et al 2000;Suo et al 2002;Witton et al 2003;Tovey et al 2004;Junttila et al 2005). Finally, constitutive ErbB4 signaling is coupled to apoptosis and/or growth arrest in human prostate, breast and pancreatic tumor cell lines (Williams et al 2003;Gallo et al 2006;Pitfield et al 2006). Collectively, these data indicate that ErbB4 behaves as a tumor suppressor in some contexts.…”

“…In particular, the Cyt-2 (CT-b) isoforms lack sixteen amino acids (Ser1046 through Gly1061) present in the canonical Cyt-1 (CT-a) isoforms (Elenius et al 1999). The Cyt-2 isoforms lack the tumor suppressor activity displayed by the Cyt-1 isoforms (Gallo et al 2006). Indeed, phosphorylation of a tyrosine residue (Tyr1056) absent in the Cyt-2 isoforms appears to be critical for ErbB4 tumor suppressor activity (Gallo et al 2006;Pitfield et al 2006).…”

“…The Cyt-2 isoforms lack the tumor suppressor activity displayed by the Cyt-1 isoforms (Gallo et al 2006). Indeed, phosphorylation of a tyrosine residue (Tyr1056) absent in the Cyt-2 isoforms appears to be critical for ErbB4 tumor suppressor activity (Gallo et al 2006;Pitfield et al 2006). Thus, measuring the phosphorylation of ErbB4 at Tyr1056 may be a strategy for monitoring ErbB4 tumor suppressor activity in tumor samples and cell lines and may help to resolve the roles that ErbB4 signaling plays in human malignancies.…”

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