Effect of acidosis on the properties of the glutaminase mRNA pH-response element binding protein

The pH-responsive stabilization of the rat renal glutaminase (GA) mRNA duri ng metabolic acidosis is mediated by a pH-response element (pH-RE). The pri mary pH-RE within the GA mRNA consists of a direct repeat of an 8-base aden osine and uridine-rich sequence, which binds a specific cytosolic protein, the pH-response element binding protein (REBP). The functional analysis of this system was performed in LLC-PK1-F+ cells, a pH-responsive line of porc ine proximal tubule-like cells. Cytosolic extracts of LLC-PK1-F+ cells also contain a protein that binds with high affinity to the rat GA mRNA pH-RE. The apparent binding of this protein is increased threefold in cytosolic ex tracts prepared from LLC- PK1-F+ cells that were grown in acidic medium (pH = 6.9, HCO3- = 10 mM). Extracts prepared from the renal cortex of rats tha t were made acutely acidotic also exhibit a similar increase in binding to the RNA probe that contains the direct repeat of the pH-RE. The temporal in crease in binding correlates with the temporal increase in GA mRNA. Scatcha rd analysis indicates that the increased binding is due to an increase in b oth the affinity and the maximal binding of the pH-REBP. Thus, increased bi nding of the pH-REBP to the GA mRNA may initiate its stabilization and incr eased expression during acidosis.