PP2A-B56alpha controls oncogene-induced senescence in normal and tumor human melanocytic cells

Authors: S Mannava....MA Nikiforov

Background: In most cells oncogene-induced senescence (OIS) is utilized as a tumor suppressor mechanism, preventing metastasis of mutated cells.  It is seen in malignant melanomas that cells are able to avoid OIS, allowing for proliferation.  One hypothesis is that C-MYC, a gene regulator upregulated in cancerous cells, protects oncogenic cells against OIS.  However, the mechanism in which C-MYC utilizes to suppress OIS in cancerous cells is still unknown.

Methods:

• cell proliferation assays
• cell senescence assays
• lentiviral constructs and infection
• qRT-PCR
• Immunoblotting and immunofluorescence

Results: First they were able to detect that C-MYC is elevated and maintained the level of the protein in melanoma cell lines using western blotting, qRT-PCR, and Chase half-life test.  Protein stability was then examined in cancerous cell lines, exposing the down regulation of PP2A B56-alpha, a regulator subunit that leads to the degredation of C-MYC, in cancerous cell lines.  As well, the upregulation of CIP2A, a C-MYC interacting protein that inhibits PP2A activity. It was then determined when B56-alpha was re-introduced to cancer cell lines and over expressed that the OIS phenotype was restored, with a decreased level in C-MYC protein expression not mRNA levels.  Lastly, it was shown that the depletion of B56-alpha in NHM leads to increased levels of C-MYC followed by increased resistance to OIS.

~JI