Function and Expression of CD44 during Spreading, Migration, and Invasion of Murine Carcinoma Cells

The cell surface glycoprotein CD44 is proposed as a main participant in cell adhesion and migration. We studied the function, expression, and distribution of CD44 in the invasive and metastatic F3II murine carcinoma cell line during adhesion, spreading, migration, and invasion. A mAb anti-CD44 (KM 201) dramatically blocked F3II cell adhesion on both plastic and hyaluronic acid coatings, as well as spreading on uncoated plastic surfaces (P< 0.01). KM201 mAb significantly inhibited F3II cell migration and invasion in Transwell chambers. Immunocytochemistry of spreading cells revealed that CD44 distributed in bands on the cell surface, particularly in the tip of leading edges and in the perinuclear zones of the cell membrane. CD44 antigen was never detected in filopodia or lamellipodia nor in focal adhesion-like structures, but was also detectable as strong interlamellar bands. Fully spread cells showed a decreased CD44 signal compared to cells in early stages of spreading. This decrease correlated with a reduced expression of CD44 as detected by Western blot. We also investigated the signals that may regulate CD44 expression in F3II cells. Treatment of F3II cells, with phorbol myristate acetate (PMA) or phosphatidic acid (PA, the product of PLD-dependent hydrolysis of phosphatidylcholine), significantly enhanced CD44 expression. Conversely, the treatment of F3II cells with H7, a specific PKC inhibitor, or propranolol, which blocks PA conversion to DAG, significantly decreased CD44 expression levels. These results suggest the involvement of PKC and PLD pathways in CD44 expression. These results demonstrate that CD44 plays an important role during F3II cells adhesion, spreading, migration, and invasion. In addition we provide information linking the PLD- and PKC-dependent pathways with the regulation of CD44 expression.     

Glucose homeostasis in rainbow trout fed a high-carbohydrate diet: metformin and insulin interact in a tissue-dependent manner

Carnivorous fish species such as the rainbow trout (Oncorhynchus mykiss) are considered to be "glucose intolerant" because of the prolonged hyperglycemia experienced after intake of a carbohydrate-enriched meal. In the present study, we use this species to study glucose homeostasis in fish chronically infused with the hypoglycemic agents, insulin, and metformin, and fed with a high proportion of carbohydrates (30%). We analyzed liver, skeletal muscle, and white adipose tissue (WAT), which are insulin- and metformin-specific targets at both the biochemical and molecular levels. Trout infused with the combination of insulin and metformin can effectively utilize dietary glucose at the liver, resulting in lowered glycemia, increased insulin sensitivity, and glucose storage capacity, combined with reduced glucose output. However, in both WAT and skeletal muscle, we observed decreased insulin sensitivity with the combined insulin + metformin treatment, resulting in the absence of changes at the metabolic level in the skeletal muscle and an increased potential for glucose uptake and storage in the WAT. Thus, the poor utilization by rainbow trout of a diet with a high proportion of carbohydrate can at least be partially improved by a combined treatment with insulin and metformin, and the glucose intolerance observed in this species could be, in part, due to some of the downstream components of the insulin and metformin signaling pathways. However, the predominant effects of metformin treatment on the action of insulin in these three tissues thought to be involved in glucose homeostasis remain exclusive in this species.