Intestinal insulin/IGF1 signalling through FoxO1 regulates epithelial integrity and susceptibility to colon cancer.

Obesity promotes the development of insulin resistance and increases the incidence of colitis-associated cancer (CAC), but whether a blunted insulin action specifically in intestinal epithelial cells (IECs) affects CAC is unknown. Here, we show that obesity impairs insulin sensitivity in IECs and that mice with IEC-specific inactivation of the insulin and IGF1 receptors exhibit enhanced CAC development as a consequence of impaired restoration of gut barrier function. Blunted insulin signalling retains the transcription factor FOXO1 in the nucleus to inhibit expression of Dsc3, thereby impairing desmosome formation and epithelial integrity. Both IEC-specific nuclear FoxO1ADA expression and IEC-specific Dsc3 inactivation recapitulate the impaired intestinal integrity and increased CAC burden. Spontaneous colonic tumour formation and compromised intestinal integrity are also observed upon IEC-specific coexpression of FoxO1ADA and a stable Myc variant, thus suggesting a molecular mechanism through which impaired insulin action and nuclear FOXO1 in IECs promotes CAC.

Aberrant splicing of the tumor suppressor CYLD promotes the development of chronic lymphocytic leukemia via sustained NF-κB signaling.

The pathogenesis of chronic lymphocytic leukemia (CLL) has been linked to constitutive NF-κB activation but the underlying mechanisms are poorly understood. Here we show that alternative splicing of the negative regulator of NF-κB and tumor suppressor gene CYLD regulates the pool of CD5+ B cells through sustained canonical NF-κB signaling. Reinforced canonical NF-κB activity leads to the development of B1 cell-associated tumor formation in aging mice by promoting survival and proliferation of CD5+ B cells, highly reminiscent of human B-CLL. We show that a substantial number of CLL patient samples express sCYLD, strongly implicating a role for it in human B-CLL. We propose that our new CLL-like mouse model represents an appropriate tool for studying ubiquitination-driven canonical NF-κB activation in CLL. Thus, inhibition of alternative splicing of this negative regulator is essential for preventing NF-κB-driven clonal CD5+ B-cell expansion and ultimately CLL-like disease.

Transgenic and knockout mice in diabetes research: novel insights into pathophysiology, limitations, and perspectives.

Insulin resistance and type 2 diabetes are serious public health threats. Although enormous research efforts have been focused on the pathogenesis of these diseases, the underlying mechanisms remain only partly understood. Here we review mouse phenotypes resulting from inactivation of molecules responsible for the control of glucose metabolism that have led to novel insights into insulin action and the development of insulin resistance. In addition, more sophisticated strategies to manipulate genes in mice in the future are presented.

New variants of inducible Cre recombinase: a novel mutant of Cre-PR fusion protein exhibits enhanced sensitivity and an expanded range of inducibility.

We have developed a novel inducible Cre mutant with enhanced recombinase activity to mediate genetic switching events. The protein, designated Cre*PR, is composed of a new Cre mutant at the N-terminus followed by the ligand-binding domain (LBD) of the progesterone receptor (PR). The response to low doses of inducer is significantly enhanced by elongating the C-terminus of the PR LBD from amino acid 891 to 914. The mutant Cre lacks the first 18 amino acids and contains a Val-->Ala substitution at position 336, thereby destroying a cryptic splice donor at the 3'-end of CRE: The latter mutation reduces unwanted background recombinase activity in the absence of the synthetic ligand RU486 by a factor of at least 10 to an almost undetectable level. Thus, the recombinase activity turns out to be inducible by a factor of >200. We expect Cre*PR to serve as a valuable tool for conditional expression of genes both in vitro and in vivo.