INCREASED SOLUBLE EGF AFTER ISCHEMIA IS ACCOMPANIED BY A DECREASE IN MEMBRANE-ASSOCIATED PRECURSORS

We have characterized the distribution of immunoreactive epidermal growth factor (irEGF) in control and ischemia-injured rat kidneys. Kidneys that had undergone ischemic injury contained levels of soluble irEGF that were six times those of uninjured kidneys. The predominant forms of soluble irEGF were native and des-Arg-epidermal growth factor (EGF), both of which are biologically active. Crude membrane fractions from whole kidneys were solubilized in Triton X-100 and tested for irEGF. Amounts of irEGF were slightly decreased in the ischemia-injured kidney membranes. However, when solubilized membrane fractions were digested with trypsin, which generates a single immunoreactive species which appears identical to native EGF, the amount of irEGF in control fractions increased 13-fold and the amount in injured fractions increased only 4-fold as measured by radioimmunoassay. To better characterize the membrane-associated irEGF, Triton X-100-solubilized membrane fractions from control animals were affinity purified and subjected to high-performance liquid molecular sieve chromatography. Three major peaks of material exhibited immunoreactivity to EGF antibodies, bound the EGF receptor, and stimulated [H-3]thymidine incorporation in growth-arrested fibroblasts. Trypsin digestion of the two high-molecular-mass peaks enhanced these activities. The third peak eluted with native EGF and showed no change in activity with trypsin addition. We propose that EGF is released from membrane-associated EGF precursors and can then act in an autocrine or paracrine fashion to promote cell growth after ischemia-induced acute renal failure.