Phosphorylation regulates Id3 function in vascular smooth muscle cells.

Understanding the mechanisms that regulate cell cycle progression in vascular smooth muscle cells (VSMCs) is key to understanding and modulating vascular lesion formation. Results of the present study provide the first evidence that phosphorylation of the helix-loop-helix factor Id3 in VSMCs occurs in vitro and in vivo and provides a regulatory switch controlling Id3-induced regulation of p21Cip1 and VSMC growth.

Intron retention generates a novel Id3 isoform that inhibits vascular lesion formation.

The expression of intron-containing messages has been shown to occur in a variety of diseases including lactic acidosis, Cowden Syndrome, and several cancers. However, it is unknown whether these intron-containing messages result in protein production in vivo. Indeed, intron-containing RNAs are typically retained in the nucleus, targeted for degradation, or are repressed translationally. Here, we show that during vascular lesion formation in rats, an alternative isoform of the helix-loop-helix transcription factor Id3 (Id3a) generated by intron retention is abundantly expressed. We demonstrate that Id3 is expressed early in lesion formation when the proliferative index of the neointima is highest and that Id3 promotes smooth muscle cell (SMC) proliferation and S-phase entry and inhibits transcription of the cell-cycle inhibitor p21(Cip1). Using an Id3a-specific antibody developed by our laboratory, we show that Id3a protein is induced during vascular lesion formation and that Id3a expression peaks late when the proliferative index is low or declining and extensive apoptosis is observed. Furthermore, Id3a fails to promote SMC growth and S-phase entry or to inhibit p21(Cip1) promoter transactivation. In contrast, Id3a stimulates SMC apoptosis and inhibits endogenous Id3 production. Adenoviral delivery of Id3a inhibited lesion formation in balloon-injured rat carotid arteries in vivo. These data describe a novel feedback loop whereby intron retention generates an Id3 isoform that acts to limit SMC growth during vascular lesion formation, providing the first evidence that regulated intron retention can modulate a pathologic process in vivo.

Lack of an effect of protease inhibitor use on glucose tolerance during pregnancy.

OBJECTIVE: We hypothesized that HIV-positive women on protease inhibitors (PIs) would be more likely to have an elevated glucola test result than those not on PIs. METHODS: We reviewed our database of all HIV-positive pregnant women seen at our hospital. Serum glucose was measured 1 hour following a 50-g glucola load, at approximately 26-28 weeks of gestation. Statistical analysis was performed using Student's t-test, Fisher's exact test, and the Mann-Whitney rank sum test. RESULTS: Forty-one HIV-infected pregnant women with glucola testing were seen between January 1, 1997 and March 1, 2000. Fourteen patients were on PIs at the time of glucola. One patient in each group had an abnormal glucola test result (glucose >/= 140 mg/dl); both had normal 3-hour glucose tolerance tests. The glucola test results were similar between the PI-exposed and unexposed, with a mean difference of 5.8 mg/dl (95% confidence interval 9.2-20.8 mg/dl). Two neonates (both exposed to PI) had hypoglycemia (glucose < 40 mg/dl). CONCLUSIONS: The use of PIs does not significantly increase the risk of an elevated glucola result, nor is the mean glucola result increased in the women on PIs. The finding of hypoglycemia in neonates exposed to PIs merits further investigation.