Background/Purpose:

Cancerous inhibitor of protein phosphatase 2A (CIP2A) is a recently identified oncoprotein that leads to cellular proliferation in cancer cells by stabilizing c-Myc protein. The effect of CIP2A in stabilizing c-Myc by inhibition of protein phosphatase 2A activity is a prerequisite step in tumor cell growth and in vivo tumor formation. We have previously shown that CIP2A is expressed in rheumatoid arthritis (RA) fibroblast-like synoviocytes (FLS), and that its expression is strongly associated with histopathological synovitis score and invasive function of RA FLS. The aim of this study is to investigate the effects of CIP2A on the apoptosis of RA FLS and to determine the signaling pathway through which dysfunctional apoptosis is facilitated.

Methods:

Proliferation and apoptotic activity of RA FLS following treatment with CIP2A siRNA or control siRNA were analyzed using MTT assays and Cell Death Detection ELISA kit. RA FLS was treated with CIP2A siRNA or control siRNA in 3, 6, and 9 day intervals for a Western blot analysis to determine C-Myc expression. To evaluate the signal transduction pathways engaged in apoptosis, caspase-3 activity, caspase-9 activity, PARP, and phosphorylation of the Akt kinase were analyzed by Western blot analysis.

Results:

Cell viability of RA FLS, as measured by MTT assay, was significantly lower in the CIP2A siRNA-treated group compared with the control after 7 days (p=0.022). Apoptosis of RA FLS, as measured by DNA fragmentation, was significantly higher in the CIP2A siRNA-treated group compared with the control when incubated for 3, 6 and 9 days (p= 0.029, p=0.021, p=0.043, respectively). Interestingly, c-Myc expression, as determined by Western blot analysis, did not change with the different incubation periods. CIP2A siRNA-treated FLS expressed higher level of activated caspase-3, caspase-9, and PARP (p=0.014, p=0.020, p=0.021, respectively) and lower level of phosphorylated Akt (p=0.001) compared with those treated with the control siRNA.

Conclusion:

Our data show that CIP2A expression in RA FLS is an important mediator of dysfunctional apoptosis independent of c-Myc stabilization. Expression of CIP2A may contribute to apoptotic resistance of RA FLS through activation of Akt and deactivation of caspase-3, caspase-9, and PARP. Inhibition of CIP2A may therefore constitute a novel, promising therapeutic target in RA.

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« Back to 2012 ACR/ARHP Annual Meeting

ACR Meeting Abstracts - https://acrabstracts.org/abstract/cip2a-facilitates-apoptotic-resistance-of-fibroblast-like-synoviocytes-in-rheumatoid-arthritis-independent-of-c-myc-expression/