A gene expression network analysis of the pancreatic islets from lean and obese mice identifies complement 1q like-3 secreted protein as a regulator of ß-cell function.

Secreted proteins are important metabolic regulators. Identifying and characterizing the role of secreted proteins from small tissue depots such as islets of Langerhans, which are required for the proper control of whole-body energy metabolism, remains challenging. Our objective was to identify islet-derived secreted proteins that affect islet function in obesity. Lean and obese mouse islet expression data were analyzed by weighted gene co-expression network analysis (WGCNA) to identify trait-associated modules. Subsequently, genes within these modules were filtered for transcripts that encode for secreted proteins based on intramodular connectivity, module membership, and differential expression. Complement 1q like-3 (C1ql3) secreted protein was identified as a hub gene affecting islet function in obesity. Co-expression network, hierarchal clustering, and gene-ontology based approaches identified a putative role for C1ql3 in regulating ß-cell insulin secretion. Biological validation shows that C1ql3 is expressed in ß-cells, it inhibits insulin secretion and key genes that are involved in ß-cell function. Moreover, the increased expression of C1ql3 is correlated with the reduced insulin secretion in islets of obese mice. Herein, we demonstrate a streamlined approach to effectively screen and determine the function of secreted proteins in islets, and identified C1ql3 as a putative contributor to reduced insulin secretion in obesity, linking C1ql3 to an increased susceptibility to type 2 diabetes.

Complement 1q-like-3 protein inhibits insulin secretion from pancreatic ß-cells via the cell adhesion G protein-coupled receptor BAI3.

Secreted proteins are important metabolic regulators in both healthy and disease states. Here, we sought to investigate the mechanism by which the secreted protein complement 1q-like-3 (C1ql3) regulates insulin secretion from pancreatic ß-cells, a key process affecting whole-body glucose metabolism. We found that C1ql3 predominantly inhibits exendin-4- and cAMP-stimulated insulin secretion from mouse and human islets. However, to a lesser extent, C1ql3 also reduced insulin secretion in response to KCl, the potassium channel blocker tolbutamide, and high glucose. Strikingly, C1ql3 did not affect insulin secretion stimulated by fatty acids, amino acids, or mitochondrial metabolites, either at low or submaximal glucose concentrations. Additionally, C1ql3 inhibited glucose-stimulated cAMP levels, and insulin secretion stimulated by exchange protein directly activated by cAMP-2 and protein kinase A. These results suggest that C1ql3 inhibits insulin secretion primarily by regulating cAMP signaling. The cell adhesion G protein-coupled receptor, brain angiogenesis inhibitor-3 (BAI3), is a C1ql3 receptor and is expressed in ß-cells and in mouse and human islets, but its function in ß-cells remained unknown. We found that siRNA-mediated Bai3 knockdown in INS1(832/13) cells increased glucose-stimulated insulin secretion. Furthermore, incubating the soluble C1ql3-binding fragment of the BAI3 protein completely blocked the inhibitory effects of C1ql3 on insulin secretion in response to cAMP. This suggests that BAI3 mediates the inhibitory effects of C1ql3 on insulin secretion from pancreatic ß-cells. These findings demonstrate a novel regulatory mechanism by which C1ql3/BAI3 signaling causes an impairment of insulin secretion from ß-cells, possibly contributing to the progression of type 2 diabetes in obesity.

Loss of p53 expression correlates with metastatic phenotype and transcriptional profile in a new mouse model of head and neck cancer.

Squamous cell carcinoma of the head and neck (HNSCC) is the sixth most frequent cancer worldwide. Because HNSCC is largely acquired by environmental carcinogen exposure rather than through germ line mutations, there are no known familial forms of the disease in humans nor are there inbred rodent strains prone to spontaneous head and neck tumors. Transgenic animals with inactivation of tumor suppressor genes commonly mutated in human cases of HNSCC provide attractive models for studying the pathogenesis of head and neck cancer. p53 is the most frequently inactivated tumor suppressor gene in HNSCC. We used a chemical induction protocol in mice heterozygous for the p53 gene to evaluate how p53 inactivation contributed to head and neck carcinogenesis the mouse model. Metastatic squamous cell carcinomas developed in 100% of animals. Histopathologically, the tumors ranged from well to poorly differentiated and showed many molecular features of human HNSCC. Mice carrying only one p53 allele developed tumors with significantly reduced latency compared with wild-type controls (average, 18 versus 22 weeks). Metastatic cancer cells showed complete loss of p53 expression when compared with primary tumors. Transcriptional profiling showed not only distinct genetic differences between primary and metastatic tumors, but also when cancers from heterozygous null and wild-type animals were compared. Our results provide novel insights into the molecular genetics of tumor progression in head and neck cancer.

Mechanism of telomerase repression during terminal differentiation of normal epithelial cells and squamous carcinoma lines.

Stratified squamous epithelial cells undergo an orderly process of cell cycle arrest following detachment from the basement membrane. The basal layer cells which adhere to the basement membrane express telomerase, which maintains the ends of chromosomes in this rapidly dividing population. Non-dividing suprabasal cells downregulate telomerase activity. However, the mechanisms regulating this inhibition are unknown. We examined the regulation of telomerase expression in anchorage-deprived normal human epidermal keratinocytes and squamous cell carcinoma lines. Anchorage-deprived cells underwent rapid loss of telomerase activity. Attachment loss was associated with increased ERK1 activity, G1 to S phase progression, and subsequent G2 arrest. Adhesion to collagen via specific integrin subunits inhibited ERK1 activity and telomerase repression. Loss of telomerase expression was associated with recruitment of an Rb/HDAC1 repressor complex to the -98 E2F site of the hTERT promoter. We propose a mechanism by which anchorage deprivation inhibits telomerase activity in stratified squamous epithelial cells and squamous cell carcinoma lines.

Overexpression of cell cycle regulatory proteins correlates with advanced tumor stage in head and neck squamous cell carcinomas.

Squamous cell carcinoma of the head and neck region (HNSCC) is the sixth most frequent cancer worldwide. In the USA, 30,000 new cases and 8,000 deaths are reported each year. Differences between normal epithelium and cancer cells from the upper aerodigestive tract arise from alterations in expression of specific genes controlling proliferation and immortalization. The protein products of these genes include growth factor receptors, cell cycle regulators, and tumor suppressors which affect a variety of intracellular signaling pathways. To determine how altered expression of these gene products contribute to HNSCC progression, we examined expression of epidermal growth factor receptor (EGFR), cyclins, p16INK4A, c-myc, proliferating cell nuclear antigen (PCNA), and telomerase in archival pathology specimens by immunohistochemistry. A substantial majority of HNSCC tumors showed loss of p16INK4A expression and dramatic overexpression of EGFR. Overexpression of this receptor correlated with increased cyclin A levels and high mitotic index. EGFR, cyclins A, -B1, -E, and c-myc overexpression was significantly increased in stage III and IV tumors compared to early stage cancers. hTERT was expressed in all tumors and primarily in the basal layer cells of dysplastic epithelial lesions. Suprabasal expression of hTERT was found in a significantly higher number of HNSCC cases than in dysplastic lesions. These results indicate that overexpression of cell cycle regulatory proteins correlates with advanced tumor stage in HNSCC.