Int J Med Sci 2009; 6(2):93-101. doi:10.7150/ijms.6.93
PKC and PKA Phosphorylation Affect the Subcellular Localization of Claudin-1 in Melanoma Cells
1. Laboratory of Immunology, National Institute on Aging, Baltimore, MD 21124, USA
2. Research Resources Branch, National Institute on Aging, Baltimore, MD 21124, USA
# Present Address: Laboratory of Clinical Investigation, National Institute on Aging, Baltimore, MD 21124, USA
French AD, Fiori JL, Camilli TC, Leotlela PD, O'Connell MP, Frank BP, Subaran S, Indig FE, Taub DD, Weeraratna AT. PKC and PKA Phosphorylation Affect the Subcellular Localization of Claudin-1 in Melanoma Cells. Int J Med Sci 2009; 6(2):93-101. doi:10.7150/ijms.6.93. Available from http://www.medsci.org/v06p0093.htm
Cytoplasmic expression of claudin-1 in metastatic melanoma cells correlates to increased migration, and increased secretion of MMP-2 in a PKC dependent manner, whereas claudin-1 nuclear expression is found in benign nevi. Melanoma cells were transfected with a vector expressing CLDN-1 fused to a nuclear localization signal (NLS). Despite significant nuclear localization of claudin-1, there was still transport of claudin-1 to the cytoplasm. Phorbol ester treatment of cells transfected with NLS-claudin-1 resulted in an exclusion of claudin-1 from the nucleus, despite the NLS. To ascertain whether PKC or PKA were involved in this translocation, we mutated the putative phosphorylation sites within the protein. We found that mutating the PKC phosphorylation sites to mimic a non-phosphorylated state did not cause a shift of claudin-1 to the nucleus of the cells, but mutating the PKA sites did. Mutations of either site to mimic constitutive phosphorylation resulted in cytoplasmic claudin-1 expression. Stable claudin-1 transfectants containing non-phosphorylatable PKA sites exhibited decreased motility. These data imply that subcellular localization of claudin-1 can be controlled by phosphorylation, dicating effects on metastatic capacity.
Keywords: Claudin, melanoma, metastasis, PKC, PKA