Wnt5A Regulates Expression of Tumor-Associated Antigens in Melanoma via Changes in Signal Transducers and Activators of Transcription 3 Phosphorylation

Abstract

There are currently no effective therapies for metastatic melanoma and targeted immunotherapy results in the remission of only a very small percentage of tumors. In this study, we show that the noncanonical Wnt ligand, Wnt5A, can increase melanoma metastasis in vivo while down-regulating the expression of tumor-associated antigens important in eliciting CTL responses (e.g., MART-1, GP100, and tyrosinase). Melanosomal antigen expression is governed by MITF, PAX3, and SOX10 and is inhibited upon signal transducers and activators of transcription 3 (STAT3) activation, via decreases in PAX3 and subsequently MITF expression. Increasing Wnt5A in Wnt5A-low cells activated STAT3, and STAT3 was decreased upon Wnt5A knockdown. Downstream targets such as PAX3, MITF, and MART-1 were also affected by Wnt5A treatment or knockdown. Staining of a melanoma tissue array also highlighted the inverse relationship between MART-1 and Wnt5A expression. PKC activation by phorbol ester mimicked Wnt5A effects, and Wnt5A treatment in the presence of STAT3 or PKC inhibitors did not lower MART-1 levels. CTL activation studies showed that increases in Wnt5A correspond to decreased CTL activation and vice versa, suggesting that targeting Wnt5A before immunotherapy may lead to the enhancement of current targeted immunotherapy for patients with metastatic melanoma.

A t-butyloxycarbonyl-modified Wnt5a-derived hexapeptide functions as a potent antagonist of Wnt5a-dependent melanoma cell invasion

“…It should be noted that not all melanoma metastasis express high levels of Wnt5a (13,19); this finding is of clinical relevance. With Box5 targeting, the need to screen patient's tumors for Wnt5a expression and active signaling will be required to identify those patients most likely to benefit from Box5 chemotherapy.…”

“…Given the distinct lack of therapeutics available for melanoma progression and the potency of Wnt5a to increase melanoma cell invasiveness and metastasis, we believe that inhibition of Wnt5a expression and signaling would be an excellent therapeutic approach for this disease, a concept already suggested by others (19). The promise of such a therapeutic approach is highlighted by the striking ability of Wnt5a to increase melanoma metastases in vivo (19).…”

“…The promise of such a therapeutic approach is highlighted by the striking ability of Wnt5a to increase melanoma metastases in vivo (19). To identify a compound capable of antagonizing the effects of Wnt5a in melanoma cells, we investigated the Wnt5a signaling pathway in more detail.…”

Caveolin-1 in Melanoma Progression

“…Alternatively, Wnt 5A expression in melanomas correlates with tumor progression and metastasis (McDonald and Silver 2009), and Wnt 5A has been shown to increase melanoma cell migration (Dissanayake, Wade et al 2007). Interestingly, these effects of Wnt 5A have been described both in in vitro and in vivo melanoma models (Dissanayake, Olkhanud et al 2008). In general, Wnt 5A enhances-melanoma cell migration but does so in a manner independent of the canonical Wnt/ -catenin pathway (Dissanayake, Wade et al 2007;Dissanayake, Olkhanud et al 2008;O'Connell and Weeraratna 2009).…”

Specifying protein kinase C functions in melanoma

“…In addition, TPA stimulated Wnt5a expression in melanoma cells with low metastatic potential and was required for increased Snail and decreased E-cadherin expression (Dissanayake et al, 2007). Wnt5a also reduced expression of melanocyte antigens MART-1, GP100, and tyrosinase in a PKC and STAT3-dependent manner, indicating that Wnt ⁄ PKC signaling may also be involved in immune evasion (Dissanayake et al, 2008). Note that the PKC enzyme required for the cellular effects of Wnt5a has not been demonstrated conclusively but is consistent with PKCa (Weeraratna et al, 2002).…”