Erythropoietin is the primary physiological regulator of erythropoiesis; however, in vitro studies have identified another class of mediators which appear to be important in stimulating erythroid progenitors. These factors have generally been referred to as burst-promoting activities (BPA), because they stimulate the growth of early erythroid progenitors referred to as burst-forming units-erythroid (BFU-E) which give rise to colonies of up to thousands of haemoglobinized cells. We recently reported purification of a burst-promoting activity from medium conditioned by the Mo T-lymphoblast cell line infected with human T-cell lymphotropic virus type II (HTLV-II). This purified glycoprotein of relative molecular mass (Mr) 28,000 also stimulates colony formation by more mature erythroid precursors (CFU-E) and is therefore referred to as erythroid-potentiating activity (EPA). Purified EPA specifically stimulates human and murine cells of the erythroid lineage, unlike murine interleukin-3 (IL-3) which stimulates precursor cells from all haematopoietic lineages. We report here the isolation of a complementary DNA molecular clone encoding EPA and its use in producing EPA in COS (monkey) cells and CHO (Chinese hamster ovary) cells. We also define the organization of the EPA gene in human DNA.

A number of proto-oncogenes have recently been localized to the chromosomal segments that are the breakpoints in the specific rearrangements noted in human malignant diseases. Moreover, rearranged forms of several proto-oncogenes have been identified in malignant cells; in several instances, the proto-oncogene has undergone an alteration as a result of a nonrandom chromosomal rearrangement. One proto-oncogene that has yet to be associated with human neoplastic disease is c-src, the cellular homologue of the transforming sequence of Rous sarcoma virus (RSV). By somatic cell hybridization, c-src has been mapped to chromosome 20, but its precise location was not determined. We have now mapped this gene by using in situ hybridization of the cloned human c-src probe to human mitotic chromosomes. We report here that the human genome contains two loci with strong homology to the coding regions of this oncogene, at 1p34-p36 and 20q12-q13. It is noteworthy that these chromosomal regions are frequently involved in the structural rearrangements observed in haematological malignant diseases.

The c-abl protooncogene is unusual in two respects; it has multiple, widely space N-terminal coding exons transcribed by different promoters, and it is the target of the translocations that form the Philadelphia chromosome found in cells of chronic myelogenous leukemia patients. To understand the organization of the gene in normal and chronic myelogenous leukemia patient DNA we have mapped c-abl by pulsed field gradient gel electrophoresis. We find that one of the alternative 5' exons of the gene lies at least 200 kilobases upstream of the remaining c-abl exons, posing formidable transcription and splicing problems. The 5'-most c-abl exon includes an unusually long 1,276-base-pair segment that contains 15 ATG codons and multiple short open reading frames, upstream of the abl initiator codon. Its peculiar structure suggests that c-abl may be decapitated in most chronic myelogenous leukemia patients, and we demonstrate that this is the case in the chronic myelogenous leukemia cell line K562.

Interstitial deletion or loss of chromosome 5, del(5q) or 75, is a frequent ®nding in myeloid leukemias and myelodysplasias, suggesting the presence of a tumor suppressor gene within the deleted region. In our search for this gene, we identi®ed a candidate, 5qNCA (LOC51780), which lies within a consistently-deleted segment of 5q31. 5qNCA expresses a 7.2-kb transcript with a 5286-bp open reading frame which is present at high levels in heart, skeletal muscle, kidney, placenta, and liver as well as CD34+ cells and AML cell lines. 5qNCA encodes a 191-kD nuclear protein which contains a highly-conserved C-terminus containing a zinc ®nger with the unique spacing Cys-X2-Cys-X7-His-X2-Cys-X2-Cys-X4-Cys-X2-Cys and a jmjC domain, which is often found in proteins that regulate chromatin remodeling. Expression of 5qNCA in a del(5q) cell line results in suppression of clonogenic growth. Preliminary sequence results in AML and MDS samples and cell lines has revealed a possible mutation in the KG-1 cell line resulting in a THR to ALA substitution that has not been found in over 100 normal alleles to date. We propose 5qNCA is a good candidate for the del(5q) tumor suppressor gene based on its predicted function and growth suppressive activities, and suggest that further mutational and functional study of this interesting gene is warranted. Oncogene (2001) 20, 6946 ± 6954.

Loss of heterozygosity (LOH) from the short arm of chromosome 8 (8p) is common to many human carcinomas, including those of the colon and prostate. It localizes to two discrete regions, 8p21 and 8p22. This suggests the presence of at least two tumor suppressor genes (TSGs) on this chromosome arm. Human breast cancers show consistent 8p deletions in cytogenetic studies, chromosome 8 aneusomy and isochromosome 8q, indicating that the relevant gene(s) may play a role, but the results of molecular analyses of chromosome 8 in breast cancer have been variable. We present here data for 8p LOH in an unselected series of human breast cancers with the use of three CA-repeat markers that showed high rates of LOH in other tumors. All cases were informative for at least one marker, and LOH was seen in 11 of 20 cases (55%). LOH was more frequent for the 8p22 markers D8S254 and D8S133 than for NEFL in 8p21. Regional metastases of the tumors showed allele profiles identical to those of their primaries regardless of whether there was LOH or retention of alleles. One case of microsatellite instability (RER+) was seen. LOH did not correlate with receptor status, ploidy, percentage of cells in S phase, or tumor size: We observed LOH at equal rates in small (< 2 cm) and in larger (> 2 cm) tumors. The data suggest that LOH from 8p is frequent in human breast cancers and that loss of the putative 8p TSG may be an important event in early stage breast cancer.