Abstract 2872: Induction of autophagy in hypoxic HT29 cells requires functional JNK1

Abstract

Abstract BACKGROUND: Hypoxic HT29 colon cancer cell lines exhibit higher sensitivity to oxaliplatin when SEK1 function is impaired and higher resistance when MKK7 is down regulated (which in turn, cause more profound inhibition of JNK activation). We observed differential effects of JNK1/JNK2 modulation on oxaliplatin sensitivity of hypoxic HT29 cells to oxaliplatin treatment that implied a pro-survival function for JNK1. Further, we have shown that both oxaliplatin- and hypoxia-induced autophagy in these cells is diminished in the presence of JNK inhibitor SP600125, and that the cells are sensitized thereby. PURPOSE: Here we investigate further how modulation of signaling through JNK influences autophagy in hypoxic HT29 cells treated with oxaliplatin, and expand the cellular model to additional colon cancer cell lines. We created a panel of HT29-derived cell lines stably expressing dominant negative constructs for SEK1 (HTS13), MKK7 (HTM9), JNK1 (HTJ1.3) and JNK2 (HTJ2.2). We also utilized 6 colon cancer cell lines (HCT116, LoVo, RKO1, SW480, DLD1 and HCT15) in which a dominant negative construct for JNK1 was introduced by viral delivery. RESULTS: Our data demonstrate that in HTJ1.3 cells, hypoxic induction of autophagy is impaired. Silencing of JNK2 in these cells by viral delivery of shRNA does not affect either autophagy induction, or sensitivity to oxaliplatin. Downregulation of up-stream activators of JNK, as in the dnSEK1 or dnMKK7 derivatives, similarly does not affect autophagy induction, while still demonstrating differential effects on activation of JNK isoforms and its major target, c-Jun. Finally, we show that colon cancer cell lines differ in their ability initiate autophagy under hypoxia. Correspondingly, the introduction of dominant negative JNK1 causes some enhancement of oxaliplatin cytotoxicity in LoVo, RKO1 and HCT15 cell lines, which all demonstrate a greater propensity to autophagy under these circumstances. CONCLUSIONS: Our data demonstrate that JNK1 plays a central role in autophagy induction under hypoxic conditions. Knockdown of JNK1 renders HT29 cells more sensitive to hypoxia due to impaired autophagy induction, and JNK2 is unable to substitute for JNK1 under these conditions. Our results also imply involvement of alternative JNK1 activators in autophagy induction by hypoxia. Finally, induction of autophagy and enhancement of oxaliplatin cytotoxicity, by this mechanism, appear to be model-specific in colon cancer. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 2872. doi:10.1158/1538-7445.AM2011-2872