Background:
Tumors and tumor cell lines from two patients with small cell lung carcinoma (sclc) (one with and one without hyponatremia) were studied. ectopic production and prohormone processing of atrial natriuretic peptide (anp) were investigated to determine if a biologically active peptide was produced in a tumor cell line from a patient with hyponatremia and no evidence of arginine vasopressin (avp) production.
Methods:
Ribonuclease (rnase) protection assays were performed on mrna isolated from tumors and tumor cell lines established from two sclc patients, one with and one without hyponatremia. cellular extracts and conditioned media were studied using reversed-phase high performance liquid chromatography (hplc) to determine the immunoreactive form of anp. tumor cell line sonicates were studied for subcellular localization of enzymatic activity that cleaved pro-anp peptide substrates.
Results:
Rnase protection assays showed a 200-base pair protected fragment in the mrna isolated from the tumor and tumor cell line from the patient with hyponatremia (patient 4). hplc characterization of the cellular extract and conditioned medium from the tumor and tumor cell line from patient 4 demonstrated anp immunoreactivity in the same fraction as anp- (s99-y126). the tumor cell line extract that localizes to a subcellular fraction enriched for lysosomes and secretory organelles contains a 60-kilodalton molecular weight protein with enzyme activity that hydrolyzes synthetic pro-anp substrates and catalyzes the formation of anp-(s99-y126).
Conclusions:
A tumor cell line from a patient with hyponatremia was able ectopically to produce, process, and secrete anp in the same immunoreactive form as the biologically active molecule. preliminary studies show that tumor cell line nci-h1284 contains an enzyme that can cleave precursors at the same amino acid sequences needed to produce anp-(s99-y126) from pro-anp.