The structure and expression of the c-myc oncogene were examined in 29 primary human colon adenocarcinomas. Dot blot hybridization of total RNA showed that 21 tumors (72%) had considerably elevated expression of c-myc (5-to 40-fold) relative to normal colonic mucosa. These data were corroborated by Northern blots of polyadenylated RNA, which showed a 2.3-kilobase transcript. Southern analysis of the c-myc locus in these tumors indicated the absence of amplification or DNA rearrangement in a 35-kilobase region encompassing the gene. In a parallel study, elevated expression of c-myc without amplification or DNA rearrangement was also observed in three of six colon carcinoma cell lines examined; in addition, unlike a normal colon cell line control, these three cell lines exhibited constitutive, high-level expression of the gene during their growth in cultures. These results indicate that elevated expression of the c-myc oncogene occurs frequently in primary human colon carcinomas and that the mechanism involved in the regulation of c-myc expression is altered in tumor-derived cell lines.

c-myc is the cellular gene homologous to the transforming sequence of MC29, an acute avian retrovirus. The human c-myc gene was cloned and used to study the structure and expression of c-myc in a variety of human hematopoietic malignancies. In a careful study of 106 patients, c-myc RNA was found to be expressed at elevated levels in tumor cells of 17 leukemia patients and five lymphoma patients. The c-myc gene was found to be rearranged in two lymphomas, an African Burkitt's lymphoma and a non-Hodgkins lymphoma in leukemic phase. The Burkitt's rearrangement involved the insertion of new DNA sequences upstream from the c-myc 5' coding region, presumably replacing the normal c-myc transcriptional promoter. None of the other 104 patients, including 20 with elevated myc expression, exhibited any evidence of a genetic rearrangement involving the c-myc gene. Our results show that there is a subset of hematopoietic malignancies characterized by elevated expression of c-myc. This elevated expression in most cases is not due to obvious genetic changes (rearrangement, amplification) at the c-myc locus nor to chromosomal translocations in the vicinity of this gene.

The presence of immunoreactive bombesin in a human lung small-cell carcinoma grown in nude mice was established by several criteria: (i) Radioimmunoassay of tissue extracts for bombesin revealed approximately 6.5 pmol/g of tissue; (ii) bombesin was found in 12-14% of the tumor cells by immunohistochemical localization; (iii) gel filtration ofsmall-cell carcinoma extract on Sephadex G-75 and Bio-Gel P-4 gave only a single peak ofimmunoreactivity, which occurred at the elution volume ofbombesin; and (iv) reverse-phase HPLC of acid-solubilized extracts separated the immunoreactive material into three discrete peaks, one of which eluted with a retention time identical to that of synthetic bombesin. Small oat-cell carcinoma accounts for 10-25% of identifiable human lung cancers (1). This neoplasm is characterized by a rapid growth rate and a propensity to metastasize (1) and is frequently a source for "ectopic" hormone production (1-7). Many of the clinical symptoms manifested by patients with small-cell carcinoma (SCC) can be attributed to increased levels ofectopic hormones (5-7). For example, the syndrome of inappropriate secretion of antidiuretic hormone is apparently due to [Arg]vasopressin (5,6,8), whereas Cushing syndrome is considered to be caused by ectopic adrenocorticotropin (ACTH) formation and secretion, which is nonsuppressible by dexamethasone (3, 5, 7). Other symptoms may be due to the presence ofpresently unknown or undiscovered peptide hormones. In this regard, bombesin, a tetradecapeptide from anuran skin, elicits numerous physiological and pharmacological responses (9, 10) that resemble some of the clinical symptoms observed for SCC.(5, 11). Bombesin-like immunoreactivity was detected in numerous mammalian tissues (12-20), including human fetal and neonatal lung, but is apparently absent from adult lung (21). Because many immunological and enzymological changes that appear in tumors resemble those normally associated with fetal tissues, it seemed reasonable to evaluate the presence of bombesin in a lung neoplasm noted for ectopic hormone production. Bombesin in a human lung SCC grown in nude mice was demonstrated by (i) immunohistochemical localization of this peptide in the tumor, (ii) its quantitation in extracts by radioimmunoassay, and (iii) analysis by gel-filtration chromatography and reverse-phase HPLC. MATERIALS AND METHODSTumor. A SCC resected from a 51-year-old man with few apparent clinical endocrinopathies was propagated subcutaneously in athymic (nude) mice by Reid et al. (22) and generously supplied by G. Sato (University of California, San Diego). Tumors from two separate passages were analyzed separately. The tumors, 8.71 and 6.36 g wet weight, were removed and sectioned for histology, and the remainders of each were minced at 10C. They were homogenized in 5 ml of ice-cold 0.01 M sodium phosphate buffer, pH 6.8, containing 1 mM phenylmethylsulfonyl fluoride. The homogenate was slowly added to 25 ml of boiling water, boiled 30 min, and cooled on ice; then formic acid was ad...

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Human colorectal carcinomas frequently express elevated levels of c-myc mRNA in the absence of a gross genetic change at the c-myc locus. To test the hypothesis that these tumors are defective in a gene function necessary for the regulation of c-myc expression, we fused an osteosarcoma cell line that exhibits normal c-myc regulation with two colon carcinoma cell lines that express deregulated levels of c-myc mRNA. The levels of c-myc transcripts in all of the hybrid clones examined were normal and were induced normally by a mitogenic stimulus. Since rates of c-myc mRNA turnover in the colon carcinoma cells were found to be comparable to those in normal cells, increased message stability cannot account for the increased steady-state levels of transcripts. Our findings suggest that loss of function of a trans-acting regulator is responsible for the deregulation of c-myc expression in a major fraction of colorectal carcinomas.