Cathelicidin-encoding Lactococcus lactis promotes mucosal repair in murine experimental colitis.

BACKGROUND AND AIM: The preventive effect of intrarectal administration of mouse cathelicidin (mCRAMP) and oral administration of mCRAMP-encoding Lactococcus lactis (N4I) has been shown in murine experimental colitis. It is pivotal to understand the ability of N4I whether it can promote mucosal repair in existing colitis. METHODS: Mice with dextran sulfate sodium-induced ulcerative colitis (UC) were treated orally with L. lactis or its transformed strain with or without nisin induction. The body weight, clinical symptoms, and histological changes of colonic tissues were determined. Sulfasalazine was used as a reference drug. Young adult mouse colon cells were used to further elucidate the direct action and possible mechanisms of mCRAMP to promote colonic wound repair. RESULTS: Results showed that N4I could improve the clinical symptoms, maintain crypt integrity and preserve mucus-secreting layer in colitis animals. The preparation also could prevent cell death and promote cell proliferation. In contrast, effective dose of sulfasalazine only alleviated clinical symptoms but not the mucosal damage and repair in the colon. In vitro study further showed that mCRAMP could directly promote wound repair by accelerating cell migration but not cell proliferation through the GPCR/MAPK pathway. CONCLUSIONS: mCRAMP-encoding L. lactis could be a potential therapeutic preparation better than the traditional anti-inflammatory agent in the treatment of UC.

FK-16 derived from the anticancer peptide LL-37 induces caspase-independent apoptosis and autophagic cell death in colon cancer cells.

Host immune peptides, including cathelicidins, have been reported to possess anticancer properties. We previously reported that LL-37, the only cathelicidin in humans, suppresses the development of colon cancer. In this study, the potential anticancer effect of FK-16, a fragment of LL-37 corresponding to residues 17 to 32, on cultured colon cancer cells was evaluated. FK-16 induced a unique pattern of cell death, marked by concurrent activation of caspase-independent apoptosis and autophagy. The former was mediated by the nuclear translocation of AIF and EndoG whereas the latter was characterized by enhanced expression of LC3-I/II, Atg5 and Atg7 and increased formation of LC3-positive autophagosomes. Knockdown of Atg5 or Atg7 attenuated the cytotoxicity of FK-16, indicating FK-16-induced autophagy was pro-death in nature. Mechanistically, FK-16 activated nuclear p53 to upregulate Bax and downregulate Bcl-2. Knockdown of p53, genetic ablation of Bax, or overexpression of Bcl-2 reversed FK-16-induced apoptosis and autophagy. Importantly, abolition of AIF/EndoG-dependent apoptosis enhanced FK-16-induced autophagy while abolition of autophagy augmented FK-16-induced AIF-/EndoG-dependent apoptosis. Collectively, FK-16 induces caspase-independent apoptosis and autophagy through the common p53-Bcl-2/Bax cascade in colon cancer cells. Our study also uncovered previously unknown reciprocal regulation between these two cell death pathways.

miRNAs in gastrointestinal and liver cancers: their perspectives and clinical applications.

MicroRNAs (miRNAs) are small non-coding RNAs that regulate gene expression post-transcriptionally. They have been found to be dysregulated in many pathological conditions including cancer and play an important role during the progression of such disease. Recent efforts have been directed in translating the primary findings of miRNAs into clinical uses. This article gives a general overview on the potential of miRNAs as diagnostic and prognostic markers and also as therapeutic targets for gastrointestinal and liver cancers in animals and humans. Other contributors in this special series would focus in discussing the roles of specific miRNAs and their pathogenic mechanisms and therapeutic applications in different types of cancer in the gastrointestinal tract and liver.

Host immune defense peptide LL-37 activates caspase-independent apoptosis and suppresses colon cancer.

Cathelicidins are a family of bacteriocidal polypeptides secreted by macrophages and polymorphonuclear leukocytes (PMN). LL-37, the only human cathelicidin, has been implicated in tumorigenesis, but there has been limited investigation of its expression and function in cancer. Here, we report that LL-37 activates a p53-mediated, caspase-independent apoptotic cascade that contributes to suppression of colon cancer. LL-37 was expressed strongly in normal colon mucosa but downregulated in colon cancer tissues, where in both settings its expression correlated with terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling-positive apoptotic cells. Exposure of colon cancer cells to LL-37 induced phosphatidylserine externalization and DNA fragmentation in a manner independent of caspase activation. Apoptogenic function was mediated by nuclear translocation of the proapoptotic factors, apoptosis-inducing factor (AIF) and endonuclease G (EndoG), through p53-dependent upregulation of Bax and Bak and downregulation of Bcl-2 via a pertussis toxin-sensitive G-protein-coupled receptor (GPCR) pathway. Correspondingly, colonic mucosa of cathelicidin-deficient mice exhibited reduced expression of p53, Bax, and Bak and increased expression of Bcl-2 together with a lower basal level of apoptosis. Cathelicidin-deficient mice exhibited an increased susceptibility to azoxymethane-induced colon tumorigenesis, establishing pathophysiologic relevance in colon cancer. Collectively, our findings show that LL-37 activates a GPCR-p53-Bax/Bak/Bcl-2 signaling cascade that triggers AIF/EndoG-mediated apoptosis in colon cancer cells.

Antibacterial peptides and gastrointestinal diseases.

Defensins and cathelicidins are small cationic peptides produced by neutrophils and epithelial cells. They are highly expressed during infection. The role of constitutive and inducible antibacterial peptides has been extensively studied over the recent years; especially in the gastrointestinal (GI) tract, where the balance between the luminal bacteria and antibacterial peptides is crucial in the maintenance of a healthy GI tract. There are reports showing that the expressions of defensins and cathelicidins in the gut are dysregulated in various disease states. They could participate in the development of different disorders ranging from inflammation to cancer. Experimental findings showed that supplementation with animal cathelicidin promoted gastric ulcer healing in rats and suppressed tumorigenesis of gastric cancer in mice. Mouse cathelicidin could alleviate murine colitis by preserving mucus content and suppression of apoptosis. Other clinical applications for these antibacterial peptides are awaiting for further studies.