Abstract 4171: Lipid metabolism-independent role of apolipoprotein (E) levels in colon carcinogenesis through a regulating inflammation and active β-catenin

Apolipoprotein E (ApoE) is critically important for cholesterol metabolism and lipid homeostasis. Polymorphisms in the ApoE gene have been implicated in the development of colon cancer and these polymorphisms may be used as risk indicators for the disease. Accruing evidence suggests new lipid metabolism-independent functions for ApoE both in inflammation and cardiovascular diseases. Ironically, ApoE was shown to up-regulate cyclooxygenase-2 in vascular smooth muscle cells and given the critical role of the COX-2 in colon carcinogenesis, these results suggest a pro-colon cancer function for the lipoprotein. In the present study, we show that a mere deletion of ApoE promotes systemic inflammation as assessed by TNF-α level in sera of mice under a regular diet. Concomitantly, TNF-α mRNA levels were significantly higher in the colon of ApoE-/- mice suggestive of localized inflammation. In contrast to smooth muscle cells, in vitro studies with primary colon epithelial cells (CECs) show that ApoE-deficiency substantially increased COX-2 expression in response to oxidized (ox)LDL both at the protein and mRNA levels. OxLDL-induced expression of COX-2 in WT CECs was highly sensitive to PP2 treatment, a Src inhibitor, and to LY294002, a pan-PI3K inhibitor. Surprisingly, while oxLDL-induced COX-2 expression was sensitive to PI3K inhibition, its sensitivity to Src inhibition was minimal suggesting that ApoE deficiency may promote COX-2 expression through a Src-independent mechanism. Similarly to COX-2, ApoE-deficiency also enhanced basal and ox-LDL-induced expression of MCP-1, IL-1β, ICAM-1, and VCAM-1. Using a cohort of colon cancer patients and healthy controls, we show that the overall levels of ApoE in sera of colon cancer patients were significantly lower than those of healthy controls (p = 0.0028). We have utilized ApcMin mice, well-characterized mouse model of intestinal tumor. Using this genetic background, we have generated ApoE+/- and ApoE-/- lines which were utilized in this study. We found that inhibition of ApoE through gene heterozygosity led to ∼50% reduction in the level of ApoE protein and a significant increased the number tumors in these mice compared to their wildtype counterparts. These changes in tumor burden were accompanied by slight changes in the lipid profiles of the ApoE+/- mice. Surprisingly however, when examining the results of ApoE-/-, we found that the tumor burden was not increased over that seen in the ApoE heterozygous mice, but the lipid profiles were elevated dramatically. This suggests that the mechanism through which ApoE affects lipid metabolism is separate from that which is involved in the formation of colon tumors. This aggravation of the tumor burden may be associated with a stimulus-independent increase in the levels of the active form of β-catenin. These results suggest that ApoE deficiency may be informative for the risk of developing colon cancer.

Citation Format: Abdelmetalab F. Tarhuni, Ali H. El-Bahrawy, Hogyoung Kim, Youssef Errami, Mohamed A. Ghonim, Mohamed Alwan, Samar M. Hammad, Venkat N. Subramaniama, Ramadan A. Hemeida, Amarjit S. Naura, Hamid A. Boulares. Lipid metabolism-independent role of apolipoprotein (E) levels in colon carcinogenesis through a regulating inflammation and active β-catenin. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 4171.

Apoptotic DNA fragmentation may be a cooperative activity between caspase-activated deoxyribonuclease and the poly(ADP-ribose) polymerase-regulated DNAS1L3, an endoplasmic reticulum-localized endonuclease that translocates to the nucleus during apoptosis

Caspase-activated DNase (CAD) is the most favorable candidate for chromatin degradation during apoptosis. Ca(2+)-dependent endonucleases are equally important in internucleosomal DNA fragmentation (INDF), including the PARP-1-regulated DNAS1L3. Despite the elaborate work on these endonucleases, the question of whether these enzymes cooperate during INDF was not addressed. Here, we show a lack of correlation between INDF and CAD expression levels and inactivation by cleavage of its inhibitor (ICAD) during apoptosis. The cells that failed to induce INDF accumulated large amounts of 50-kb breaks, which is suggestive of incomplete chromatin processing. Similarly, INDF was blocked by Ca(2+) chelation without a block in ICAD cleavage or caspase-3 activation, which is consistent with the involvement of CAD in 50-kb DNA fragmentation and its Ca(2+) independence. However, DNAS1L3 expression in INDF-deficient cells promoted INDF during apoptosis and was blocked by Ca(2+) chelation. Interestingly, expression of DNAS1L3 in ICAD-deficient cells failed to promote tumor necrosis factor α-induced INDF but required the coexpression of ICAD. These results suggest a cooperative activity between CAD and DNAS1L3 to accomplish INDF. In HT-29 cells, endogenous DNAS1L3 localized to the endoplasmic reticulum (ER) and translocated to the nucleus upon apoptosis induction but prior to INDF manifestation, making it the first reported Ca(2+)-dependent endonuclease to migrate from the ER to the nucleus. The nuclear accumulation of DNAS1L3, but not its exit out of the ER, required the activity of cysteine and serine proteases. Interestingly, the endonuclease accumulated in the cytosol upon inhibition of serine, but not cysteine, proteases. These results exemplify the complexity of chromatin degradation during apoptosis.

Prophylactic role of curcumin in dextran sulfate sodium (DSS)-induced ulcerative colitis murine model

We have addressed in this study the possible protective role of the main principle of turmeric pigment; curcumin on a murine model of ulcerative colitis (UC). Colitis was induced by administration of dextran sulfate sodium (DSS) (3% W/V) in drinking water to male Swiss albino rats for 5 consecutive days. DSS challenge induced UC model that was well characterized morphologically and biochemically. DSS produced shrinkage of colon length and increased the relative colon weight/length ratio accompanied by mucosal edema and bloody stool. Histologically, DSS produced submucosal erosions, ulceration, inflammatory cell infiltration and crypt abscess as well as epithelioglandular hyperplasia. The model was confirmed biochemically, and the test battery entailed elevated serum tumor necrosis factor (TNF-alpha) and colonic activity of myleoperoxidase (MPO). Colonic glutathione-S-transferase (GST) activity and its substrate concentration; GSH, were notably reduced, while lipid peroxidation, expressed as malondialdehyde (MDA) level, and total nitric oxide (NO) were significantly increased. Prior administration of curcumin (100mg/kg, IP) for 7 consecutive days ahead of DSS challenge mitigated the injurious effects of DSS and ameliorated all the altered biochemical parameters. These results suggest that curcumin could possibly have a protective role in ulcerative colitis probably via regulation of oxidant/anti-oxidant balance and modulation of the release of some inflammatory endocoids, namely TNF-alpha and NO.