The Principal Investigator noted in preliminary studies that a patient with severe insulin resistance expressed increased amounts of a specific surface protein called PC-1. Subsequent purification and partial sequencing led to the identification of PC-1 as nucleotide pyrophosphatase/alkaline phosphatase. A surface ectoenzyme of uncertain function but perhaps involved in recycling of nucleotide phosphates by multiple cell types. The enzymatic activity is on the extracellular domain of the protein which has a single membrane spanning domain and a short intracellular tail. This protein exists as a homodimer is coded for by chromosomal region 6q22-q23. In fibroblasts from the proband patient tyrosine auto-phosphorylation of the insulin receptor and 2 deoxyglucose uptake were reported less responsive to insulin compared with controls and PC-1 content in the proband s cell were elevated approximately 10-fold. Subsequent studies in fibroblasts from 9 NIDDM subjects showed a wide range of PC-1 content but levels were elevated in 7 of 9. Overexpression (approx 10 fold) of PC-1 in several fibroblasts lines led to diminished insulin-stimulated receptor auto-phosphorylation. This effect was not seen with either the EGF or IGF-1 receptor. These studies in fibroblasts led to further preliminary studies in human muscle and adipose exploring the relationship between PC-1 content and insulin resistance. Based on the correlations observed in healthy controls and obese individuals the PI hypothesizes that PC-1 may be involved in the insulin resistance in at least some forms of NIDDM due to impaired receptor auto-phosphorylation. He proposes to examine the relationship between in vivo insulin sensitivity (minimal model) and in vitro insulin sensitivity as measured by insulin stimulation of glucose transport and activation of receptor tyrosine kinase. Studies will be done in non-diabetic individuals with a wide range of insulin sensitivity and obese individuals. Correlations will also be sought between insulin sensitivity in adipocytes and fibroblasts and PC-1 content of these tissues. The PI will then determine increases in PC-1 and impairments in receptor tyrosine kinase observed in vivo persist in cultured cells (fibroblasts and muscle) . Finally, the PI and collaborators will address whether interventions to improve insulin sensitivity in vivo (weight reduction and exercise) alter PC-1 expression and tyrosine kinase activity in humans.
