Expression of N‐terminally truncated isoforms of CDP/CUX is increased in human uterine leiomyomas

Abstract

Genetic analyses and mRNA expression studies have implicated CUTL1 as a candidate tumor-suppressor gene in uterine leiomyomas and breast cancers. However, modulation of CDP/Cux, the protein encoded by CUTL1, does not agree with this notion. The activity of CDP/Cux, which is the DNA binding subunit of HiNF-D, was upregulated as normal cells progressed into S phase and constitutively elevated in several tumor cell lines. Activation of CDP/Cux at the G 1 /S transition involved the proteolytic processing of the protein to generate a shorter isoform. Uterine leiomyomas represent a unique reagent for molecular analysis because they are resected as homogenous tumor tissue together with the adjacent normal myometrium and they are often very large. In the present study, proteins were isolated from 16 pairs of matched tumors and adjacent myometrium and analyzed by Western blot and electrophoretic mobility shift assays. Strikingly, in 11/16 tumors, the steady-state level of small CDP/ Cux isoforms was increased compared to normal control tissue. Where tested, a corresponding increase in CDP/Cux stable DNA binding activity was observed. DNA sequencing analysis of CUTL1 cDNAs from 6 leiomyomas, including 4 with LOH of CUTL1, did not reveal any gross rearrangement or point mutations. Altogether these findings suggest that CUTL1 is probably not the tumor suppressor on 7q22. Moreover, the frequent increase in smaller CDP/Cux isoforms indicates that molecular events associated with the truncation of CDP/Cux proteins may be selected in uterine leiomyomas.

The p110 Isoform of the CDP/Cux Transcription Factor Accelerates Entry into S Phase

“…Thus, our results indicate that p110 CDP/Cux cannot on its own drive cells into S phase, but it can accelerate cell cycle progression without apparent negative consequences for the cells. These properties clearly distinguish p110 CDP/Cux from some members of the E2F family and suggest that overexpression of CDP/Cux in various tumors and in particular of its short isoforms must provide cancer cells with a growth advantage (17,46). Indeed, transgenic mice expressing short CDP/Cux isoforms display increased susceptibility to various types of cancers (C. Cadieux, S. Fournier, A. C. Peterson, B. J. Bedell, and A. Nepveu, submitted).…”

CUX1, a haploinsufficient tumour suppressor gene overexpressed in advanced cancers

“…Although early cytogenetic studies and polymorphic marker analyses clearly pointed to the presence of a tumour suppressor gene on 7q22.1, the implicated gene was not rapidly identified. CUX1 and a few other genes were consistently present within the smallest deleted region, but no mutation was found in the remaining allele of any of these genes [7][8][9][10] . These results eventually led to the idea that inactivation of the tumour suppressor on 7q22.1 may not conform to the Knudson two-hit model.…”

“…Recent genetic mapping and expression analyses pointed to CUX1 as the tumour suppressor that is the target of loss-of-heterozygosity (LOH) on chromosome 7q22.1 . In cancers with CUX1 LOH, no mutations have been found in the remaining allele [7][8][9][10] and, in tested cases, CUX1 was expressed, albeit at a reduced level 4,5,11 . However, inactivating point mutations were shown in 1-5% of cancers in which the two CUX1 alleles are present 11 (FIG.…”

Proteolytic Processing of Cut Homeobox 1 by Neutrophil Elastase in the MV4;11 Myeloid Leukemia Cell Line

“…In contrast, the fulllength protein did not have any effect in the same assays. 5 Whereas proteolytic processing of CUX1 was shown to be tightly regulated during cell cycle progression in normal cells, increased processing of CUX1 was reported both in primary human uterine leiomyomas and several cancer cell lines (23,24). In transgenic mice, forced expression of short CUX1 proteins enhanced the susceptibility to various malignancies, in particular in the myeloid cell lineage (25).…”

“…In uterine leiomyomas, p110 CUX1 was frequently expressed at a higher level in the tumor than in the adjacent myometrium (23). In many cancer cell lines, increased expression and activity of nuclear cathepsin L was found to result in a higher ratio of processed over the full-length CUX1 protein (24).…”