The LIMD1 protein bridges an association between the prolyl hydroxylases and VHL to repress HIF-1 activity.

There are three prolyl hydroxylases (PHD1, 2 and 3) that regulate the hypoxia-inducible factors (HIFs), the master transcriptional regulators that respond to changes in intracellular O(2) tension. In high O(2) tension (normoxia) the PHDs hydroxylate two conserved proline residues on HIF-1α, which leads to binding of the von Hippel-Lindau (VHL) tumour suppressor, the recognition component of a ubiquitin-ligase complex, initiating HIF-1α ubiquitylation and degradation. However, it is not known whether PHDs and VHL act separately to exert their enzymatic activities on HIF-1α or as a multiprotein complex. Here we show that the tumour suppressor protein LIMD1 (LIM domain-containing protein) acts as a molecular scaffold, simultaneously binding the PHDs and VHL, thereby assembling a PHD-LIMD1-VHL protein complex and creating an enzymatic niche that enables efficient degradation of HIF-1α. Depletion of endogenous LIMD1 increases HIF-1α levels and transcriptional activity in both normoxia and hypoxia. Conversely, LIMD1 expression downregulates HIF-1 transcriptional activity in a manner depending on PHD and 26S proteasome activities. LIMD1 family member proteins Ajuba and WTIP also bind to VHL and PHDs 1 and 3, indicating that these LIM domain-containing proteins represent a previously unrecognized group of hypoxic regulators.

Interstitial deletions including chromosome 3 common eliminated region 1 (C3CER1) prevail in human solid tumors from 10 different tissues.

A human chromosomal segment regularly lost during tumor formation of microcell hybrids in SCID mice has been mapped to 3p21.3. This segment, called chromosome 3 common eliminated region 1 (C3CER1, also referred to as CER1), may harbor multiple tumor-suppressor genes. Because it was found that similar regions were eliminated in an inter- and intraspecies system and in two tumor types (mouse fibrosarcoma and human renal cell carcinoma), we hypothesized that the importance of C3CER1 would transgress tissue specificity, that is, it could occur in tumors derived from multiple tissues. To evaluate the loss of C3CER1 in various human tumor types, we conducted loss of heterozygosity (LOH) analysis of 576 human solid tumors from 10 different tissues and compared the frequency of deletion in the C3CER1 area to that in two other regions on 3p: the FHIT/FRA3B region, at 3p14.2, and the VHL region, at 3p25.3. Deletions were detected in the C3CER1 region in 83% of informative tumors. Half (47%) the LOH-positive tumors showed LOH at all informative markers, indicating a large deletion. The other half (53%) had a discontinuous LOH pattern, suggesting interstitial deletions or breakpoints. The proportion of tumors with C3CER1 deletions was high in all tumor types investigated, ranging from 70% to 94%, except for the soft-tissue sarcomas (40%). In the VHL and FHIT regions, deletions were observed in 73% and 43%, respectively, of the tumors. Of the three 3p regions analyzed, the highest deletion frequency was observed in the C3CER1 region. Furthermore, we demonstrated that the interstitial deletions including C3CER1 prevail over 3p14.2-pter losses in solid tumors.

Loss of heterozygosity at the FHIT gene in different solid human tumours and its association with survival in colorectal cancer patients.

BACKGROUND: Genomic alterations and abnormal expression of the FHIT gene have been reported for a number of cancers. FHIT encompasses FRA3B, the most common fragile site in the human genome, and is suggested to be a candidate tumour suppressor gene. MATERIALS AND METHODS: We analysed and compared the loss of heterozygosity (LOH) pattern in 397 solid human tumours from 9 different locations, using four polymorphic microsatellite markers within the gene (D3S1234, D3S1300, D3S2757 and D3S4260), and two markers (D3S1313 and D3S1600) flanking the gene. In addition, we tested whether there was an association between FHIT LOH and overall patient survival in colorectal cancer. RESULTS: LOH at the FHIT gene affecting at least one of the investigated markers was detected in 166 out of 332 informative tumours, or 50%. The highest detected LOH was in lung tumours (66%) while the lowest was in thyroid and endometrium tumours, (30% and 31%, respectively). Breakpoints were found inside the gene in all tumour types in 12-80% of the tumours with FHIT LOH depending on tumour type, and up to 41% could additionally be located adjacent to the 3' or 5' end of the FHIT gene. Thus we were able to locate breakpoints within or in the vicinity of the FHIT gene in 25-100% of different tumours with LOH. Although not statistically significant, we observed a trend towards a poorer survival of patients with FHIT LOH versus those with retention of heterozygosity. CONCLUSION: Based on our results, LOH of the FHIT gene is a common event in all tumour types analysed with a possible association with poorer survival in colorectal cancer patients. LOH at all markers analysed was, in most of the tumour types, a more common pattern of alterations than breakpoints.