---

Both c-JUN and Cyclin D1 activity is deemed critical for melanoma cell proliferation, a functionality nicely corroborated by frequently elevated expression and activity of these proteins in human melanomas. Consistently, alleviating c-JUN and Cyclin D1 function is vital to the success of anti-melanoma therapeutics.

The objective of current work is to understand the role of JNK signaling pathway in melanoma cell proliferation and survival.

The effect of JNK inhibitors SP600125 and JNK-IN-8 on the proliferation and survival of genetically highly representative human melanoma cell lines was studied in assays of proliferation and apoptosis. Changes in c-JUN and Cyclin D1 protein and mRNA levels in response to JNK and MEK inhibition were investigated through immunoblotting and qRT-PCR. Effect of JNK and MEK inhibitors on cell cycle distribution was assessed by flow-cytometry.

We demonstrate the requirement of JNK signaling in melanoma cell proliferation and survival. While JNK inhibition suppressed the expression and activity of c-JUN, it failed to suppress Cyclin D1 levels. Consistent with its inability to downregulate Cyclin D1, JNK inhibition failed to induce a G1-arrest. In contrast, the blockade of MEK-ERK signaling, although unable to persistently suppress c-JUN activity and expression, paradoxically, abated Cyclin D1 levels and triggered a G1-arrest. This previously unreported dual disconnect between JNK-Cyclin D1 and ERK-c-JUN levels was confirmed by a concomitant JNK and BRAF inhibition, which suppressed both c-JUN and Cyclin D1 levels and exhibited a heightened anti-proliferative response.

Dual disjunction between JNK-Cyclin D1 and ERK-c-JUN signaling forms basis for further investigating combined JNK and MAPK signaling blockade as a more effective therapeutic approach in human melanoma. This article is protected by copyright. All rights reserved.

This article is protected by copyright. All rights reserved.

PMID:27145925