Abstract 1350: Mitogen activated protein kinase activated protein kinase 2 (MK2) signaling in non-small cell lung carcinoma

Rationale: Apoptosis is a type of programmed cell death that occurs in eukaryotic cells. Apoptosis is thought to be regulated by caspase 3 relocalization from the cytosol into the nucleus. Recent studies in our laboratory have shown that MK2 is necessary for nuclear translocation of caspase 3 during apoptosis. Furthermore, studies in lung cancer have reported defective nuclear translocalization of caspase 3 in non-small cell lung carcinoma as a potential mechanism of resistance to apoptosis. Objective: We sought to determine if there is aberrant MK2 signaling in non-small cell lung cancer (NSCLC) and if this may play a role in cleaved caspase 3 relocalization from the cytosol into the nucleus, and thereby explaining the resistance of non-small cell lung carcinoma to undergo apoptosis. Methods: We compared two lung cancer cell lines, a non-small cell lung cancer cell line (H23 NSCLC) and a small cell lung cancer cell line (H446 SCLC) and treated them with 3.0 ug/ml etoposide for 24 hours. Etoposide is a topoisomerase inhibitor that was used to induce apoptosis. After exposure to experimental conditions, cells were lysed and proteins were analyzed by immunoblotting. Results: In response to etoposide treatment for 24 hours, cleavage of caspase-3 was observed in both H23 and H446 cell lines. An increase in cleavage of ROCK1, a cytoplasmic substrate of caspase 3 was observed in both H23, NSCLC, and H446, SCLC, cell lines. Cleavage of PARP was only observed in the H446 SCLC cell line in response to etoposide whereas the H23 NSCLC cell line exhibited no cleavage of PARP. A difference in the amount of MK2 expression was also observed between the two cancer cell lines with the H23 NSCLC cell line having the lower MK2 expression when compared with the H446 SCLC cell line. Conclusion: Caspase 3 cleavage in both cancer cell lines shows that the apoptotic machinery is active in both the H23 NSCLC and H446 SCLC cell lines. The significant increase in cleavage of ROCK1 in both H23 and H446 cell lines suggests that cleaved caspase 3 is active in the cytosol in both cell lines. PARP is cleaved in only the H446 SCLC cell line but not in H23 NSCLC cell line suggesting that caspase 3 does not translocate from the cytosol into the nucleus in the NSCLC cell line. The difference in the amount of MK2 expression between the H23 and the H446 suggests that MK2 signaling may play a vital role in relocalization of caspase 3 from the cytosol into the nucleus, similar to our prior work. Further studies are needed in order to explain the difference in the amount of MK2 expression between the two cancer cell lines. Citation Format: Oscar Paniagua-Morales, Laura Johnston, Leonid Serebreni, Gigi Liu, Paul Hassoun, Mahendra Damarla. Mitogen activated protein kinase activated protein kinase 2 (MK2) signaling in non-small cell lung carcinoma. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 1350. doi:10.1158/1538-7445.AM2014-1350