Microphthalmia-associated transcription factor suppresses invasion by reducing intracellular GTP pools

Area of Science:

• Molecular Biology
• Cancer Research
• Cell Biology

Background:

• Melanoma progression correlates with increased invasion and reduced microphthalmia-associated transcription factor (MITF).
• Downregulation of MITF is known to induce melanoma cell invasion, but the mechanisms remain unclear.

Purpose of the Study:

• To elucidate the molecular mechanisms by which MITF downregulation promotes melanoma cell invasion.
• To identify novel regulators of melanoma cell invasion linked to MITF activity.

Main Methods:

• Investigated the effects of MITF depletion on intracellular GTP levels and GTP-bound Rho GTPases (RAC1, RHO-A, RHO-C) in melanoma cells.
• Assessed invadopodia formation and cell invasion assays.
• Identified guanosine monophosphate reductase (GMPR) as a direct MITF target gene.
• Examined the role of GMPR in MITF-dependent regulation of melanoma cell invasion and tumorigenicity.
• Analyzed MITF and GMPR expression in vemurafenib-resistant melanoma cells.

Main Results:

• MITF depletion led to elevated intracellular GTP levels and increased active RAC1, RHO-A, and RHO-C.
• MITF-depleted cells exhibited increased invadopodia and enhanced invasion.
• GMPR was identified as a direct MITF target, and its repression largely explained the observed phenotypes.
• GMPR transactivation was essential for MITF-mediated suppression of invasion, tumorigenicity, and lung colonization.
• Loss of GMPR correlated with MITF downregulation in vemurafenib-resistant melanoma, contributing to increased invasion.

Conclusions:

• MITF inhibits melanoma cell invasion by suppressing guanylate metabolism through direct regulation of GMPR.
• The MITF-GMPR axis represents a novel mechanism controlling melanoma cell invasion and metastasis.
• Targeting GMPR may offer therapeutic strategies for invasive and drug-resistant melanoma.