Insulin-like growth factors are more effective than progastrin in reversing proapoptotic effects of curcumin: critical role of p38MAPK

Abstract

Singh P, Sarkar S, Umar S, Rengifo-Cam W, Singh AP, Wood TG. Insulin-like growth factors are more effective than progastrin in reversing proapoptotic effects of curcumin: critical role of p38MAPK. Am J Physiol Gastrointest Liver Physiol 298: G551-G562, 2010. First published February 4, 2010 doi:10.1152/ajpgi.00497.2009.-Progastrin and insulin-like growth factors (IGFs) stimulate hyperproliferation of intestinal epithelial cells (IECs) via endocrine/paracrine routes; hyperproliferation is a known risk factor for colon carcinogenesis. In the present study, inhibitory potency of curcumin in the presence or absence of progastrin and/or IGF-II was examined. Progastrin and IGF-II significantly increased proliferation of an immortalized IEC cell line, IEC-18, whereas curcumin decreased the proliferation in a dose-dependent manner. IGF-II was significantly more effective than progastrin in reversing antiproliferative effects of curcumin and reversed proapoptotic effects of curcumin by Ͼ80%; progastrin was relatively ineffective toward reversing proapoptotic effects of curcumin. IEC-18 clones were generated to overexpress either progastrin (IEC-PG) or hIGF-II (IEC-IGF). Proliferation of IEC-PG and IEC-IGF clones was increased, compared with that of control clones. Curcumin significantly reduced proliferation of IEC-PG, but not IEC-IGF, clones. Similarly, a human colon cancer cell line, Caco-2 (which expresses autocrine IGF-II), was relatively resistant to inhibitory effects of curcumin. However, Caco-2 cells treated with anti-IGF-II-antibodies were rendered sensitive to inhibitory effects of curcumin. Significant differences in inhibitory potency of curcumin against PG-vs. IGF-II-stimulated growth of IEC-18 cells were not reflected by differences in curcumin-mediated inhibition of activated (phosphorylated) ERKs/IKK␣/␤/p65NF-B and c-Src in wild-type (wt)IEC-18 cells, in response to the two growth factors. Surprisingly, curcumin was almost ineffective in reducing IGF-II-stimulated activation of p38MAPK but significantly reduced progastrin-stimulated phosphorylation of p38. Treatment with a p38MAPK inhibitor resulted in loss of protective effects of IGF-II against inhibitory effects of curcumin. These novel findings suggest that growth factor profile of patients and tumors may dictate inhibitory potency of curcumin and that combination of curcumin ϩ p38MAPK inhibitor may be required for reducing hyperproliferative or tumorigenic response of IECs to endocrine and autocrine IGFs.

Autocrine Secretion of Progastrin Promotes the Survival and Self-Renewal of Colon Cancer Stem–like Cells

“…3C), suggesting that progastrin did not regulate the ability of ALDH neg cells to generate ALDH high cells within this timeframe. To assess whether this lack of effect on ALDH neg cells was paralleled by a differential ability of progastrin to engage signaling in these cells, we analyzed the ability of progastrin to regulate the phosphorylation of p38MAPK, which plays a role in regulating CSC characteristics such as drug resistance (33) and is phosphorylated in response to progastrin (34,35 Endogenous progastrin depletion in ALDH high cells or treatment with recombinant progastrin, respectively, decreased or increased their sphere-forming ability (Fig. 3D and Supplementary Fig.…”

Curcumin Promotes Autophagic Survival of a Subset of Colon Cancer Stem Cells, Which Are Ablated by DCLK1-siRNA

“…Curcumin has potent anti-inflammatory, anti-bacterial and anti-cancer effects (10), but lacks solubility in aqueous solutions; bioavailable formulations have been developed (11) and are being examined in phaseI/II clinical trials (12, personal communications with Dr. Lawrence Helson). Curcumin is non-toxic at high doses (12g/day), and targets multiple oncogenic pathways (10,12–14). However, pro-apoptotic effects of curcumin are attenuated by autocrine growth factors (14).…”

“…Curcumin is non-toxic at high doses (12g/day), and targets multiple oncogenic pathways (10,12–14). However, pro-apoptotic effects of curcumin are attenuated by autocrine growth factors (14). Thus, sub-populations of cancer cells may escape inhibitory effects of curcumin; this concept was extended to CSCs in the current studies.…”

Epigenetic regulation of human DCLK-1 gene during colon-carcinogenesis: clinical and mechanistic implications

“…Experiments with mouse models of tumorogenesis have confirmed a critical role of Dclk1 in tumorigenesis, and as a CSC marker, as described below. It is important to note that overexpression of PG in either mature colonic epithelium (as in Fabp-PG mice) (19,(24)(25)(26) or in intestinal epithelial (IEC) cells (30), results in hyper proliferation of colonic crypts/cells, but does not cause neoplastic transformation (IEC-cells) or formation of colonic tumors (Fabp-PG mice) in the absence of AOM±DSS (19,(24)(25)(26)30). However, overexpression of PG in embryonic epithelial cells, allowed neoplastic transformation of the epithelial cells confirming hyper-sensitivity of multi-potent embryonic stem cells, unlike mature stem cells.…”

“…We recently reported that a subset of DCLK1 + CSCs are resistant to inhibitory effects of potent chemopreventive agents such as curcumin (31), which may explain the failure of curcumin in clinical trials with cancer patients. Even though curcumin and several chemopreventive agents have been reported to attenuate multiple inflammatory and oncogenic pathways [discussed in (30,31)], for reasons unknown, a subset of DCLK1+ colon cancer cells, survive inhibitory effects of chemopreventive/ chemotherapeutic agents by undergoing autophagy, associated with survival rather than apoptosis (31). Downregulation of DCLK1 was required in combination with chemopreventive agents for eliminating CSCs and avoiding relapse (in terms of reformation of tumorospheres from colon cancer cells) (31).…”