HLS5, a Novel RBCC (Ring Finger, B Box, Coiled-coil) Family Member Isolated from a Hemopoietic Lineage Switch, Is a Candidate Tumor Suppressor

Abstract

Hemopoietic cells, apparently committed to one lineage, can be reprogrammed to display the phenotype of another lineage. The J2E erythroleukemic cell line has on rare occasions developed the features of monocytic cells. Subtractive hybridization was used in an attempt to identify genes that were up-regulated during this erythroid to myeloid transition. We report here on the isolation of hemopoietic lineage switch 5 (Hls5), a gene expressed by the monocytoid variant cells, but not the parental J2E cells. Hls5 is a novel member of the RBCC (Ring finger, B box, coiled-coil) family of genes, which includes Pml, Herf1, Tif-1␣, and Rfp. Hls5 was expressed in a wide range of adult tissues; however, at different stages during embryogenesis, Hls5 was detected in the branchial arches, spinal cord, dorsal root ganglia, limb buds, and brain. The protein was present in cytoplasmic granules and punctate nuclear bodies. Isolation of the human cDNA and genomic DNA revealed that the gene was located on chromosome 8p21, a region implicated in numerous leukemias and solid tumors. Enforced expression of Hls5 in HeLa cells inhibited cell growth, clonogenicity, and tumorigenicity. It is conceivable that HLS5 is one of the tumor suppressor genes thought to reside at the 8p21 locus.

Hls5 regulated erythroid differentiation by modulating GATA-1 activity

“…Thus, elevated Hls5 levels inhibit the development and maturation of erythroid progenitors, which could be due to cell death, as over-expression of Hls5 can induce apoptosis. 4 To examine the effects of Hls5 on immature erythroid cells in greater detail, J2E cells 1 were infected with vector alone, or Hls5-expressing retroviruses and termed J-Hls5 or J-Hls5-myc ( Figure 1B). Confocal microscopy showed that Hls5 was present primarily in granular structures throughout the cytoplasm, a feature characteristic of RBCC/TRIM family members 6 ; however, the protein was also detected in nuclear structures ( Figure 1C).…”

“…5 Importantly, ectopic expression of Hls7/Mlf1 in J2E cells imposes a dramatic phenotypic change on the cells, rendering them monoblastoid. 2 Hls5 is a recently identified member of the RING finger, B box, coiled coil (RBCC) 4 or Tripartite motif (TRIM) family, 6 which includes PML, a gene involved in acute promyelocytic leukemia. Hls5 is expressed in a wide variety of hemopoietic cell types, including fetal liver progenitors.…”

“…3 Hls5 and Hls7 were isolated as genes markedly up-regulated in the J2E monoblastoid variants. 2,4 Hls7 is the murine orthologue of Myeloid Leukemia Factor 1 (Mlf1), a gene involved in the t(3;5), associated with acute myeloid leukemia. 5 Importantly, ectopic expression of Hls7/Mlf1 in J2E cells imposes a dramatic phenotypic change on the cells, rendering them monoblastoid.…”

“…Hls5 is expressed in a wide variety of hemopoietic cell types, including fetal liver progenitors. 4 The role of Hls5 in erythroid maturation was investigated in this study. …”

The mei-P26 Gene Encodes a RING Finger B-box Coiled-Coil-NHL Protein That Regulates Seizure Susceptibility in Drosophilia

“…Proteins with a tripartite RBCC domain nal outputs of the GF system, the dorsal longitudinal are involved in a variety of diverse cellular processes muscle and tergotrochanteral muscle, do not show any including ubiquitination, transcription regulation, miobvious abnormalities in su(eas)16 flies (data not crotubule stabilization, tumorigenesis, and apoptosis shown). Thus, individual neuronal excitability does not (Xu et al 2003;Dho and Kwon 2003;Berti et al 2004; appear to be decreased in mei-P26 flies but deficits that Lalonde et al 2004;Wang et al 2004). An interesting we have not been able to measure may exist.…”