DBCCR1 mediates death in cultured bladder tumor cells

Abstract

Chromosome 9, which is often partially or fully reduced to homozygosity in bladder cancer cells, harbors several tumor suppressor loci including deleted in bladder cancer chromosome region 1 (DBCCR1) at 9q32-33. To study DBCCR1 function, stable cell lines, inducible for DBCCR1 expression by tetracycline, were made, but the DBCCR1 protein was not expressed at detectable levels. To understand the fate of DBCCR1-expressing cells, human bladder tumor cells were transiently transfected with an expression vector containing DBCCR1 fused to enhanced green fluorescent protein (EGFP). Initially, DBCCR1-EGFP-expressing cells demonstrated diffuse cytoplasmic green fluorescence with nuclear exclusion patterns. After time, the intensity level of green fluorescence increased and a granular distribution of protein became visible in the cells. At this point, cells rounded up and detached from the tissue culture dish. Cells transfected with a control vector, containing only EGFP, and partial DBCCR1-EGFP fusion constructs did not demonstrate this behavior. DBCCR1-mediated cell death in cultured tumor cells was independent of caspase-3 activation and did not result in detectable DNA strand breaks by TUNEL staining that are hallmarks of the classical apoptotic pathway.

Frequent hypermethylation of DBC1 in malignant lymphoproliferative neoplasms

“…21 However, other attempts to generate cells with stable DBC1 expression have repeatedly failed, indicating that expression of DBC1 may lead to severe growth inhibition or even cell death, at least in some cellular contexts. Indeed, Wright et al 20 showed that induced expression of DBC1 in bladder tumor cell lines induced caspase-independent cell death. Accordingly, activation of DBC1 expression may be important for the elimination of some normal cells, possibly acting as a fail-safe mechanism that is triggered in parallel with other death pathways or when other death pathways fail.…”

“…Interestingly, perforin has been shown to be involved in both familial hemophagocytic lymphohistiocytosis 18 and sporadic lymphoma by point mutations. 19 Ectopic reexpression of DBC1 in cancer cell lines with DBC1 hypermethylation elicited a range of cellular effects, including cell-cycle arrest, caspase-independent apoptosis, 20 and altered expression of key factors in the plasminogen pathway. 21 However, it is still not evident which of these DBC1 functions are essential in controlling carcinogenesis, and under which cellular circumstances they are active.…”

Molecular biology of bladder cancer

“…Losses at 9q cover 3 major deleted regions (9q22, 9q32-33, and 9q34) and one or several tumor suppressor genes may be located in them. Candidate genes therein include Netrin, TSC1, PTCH and DBCCR1 17,[42][43][44] . Allelic loss at 9q has been reported as an early occurrence in the development of bladder cancer but it has also been associated with invasive disease and with disease recurrence in superficial bladder tumors.…”

DBC1 re-expression alters the expression of multiple components of the plasminogen pathway

“…After 2 days, the inhibitory effect on clone B was nearly 50% and after 7 days more than 75%. We and others (Wright et al, 2004) have attempted to generate TCC cell lines with inducible DBC1 expression with no success, which indicates that even low-level DBC1 expression may be extremely toxic in some situations.…”

“…Our previous studies have shown that re-expression of DBC1 in bladder tumour cells has an antiproliferative effect, but this does not appear to be due to a direct effect on apoptosis (Nishiyama et al, 2001). Recently, Wright et al (2004) reported that DBC1 mediates cell death in cultured bladder tumour cells with a mechanism which is not of the classic apoptotic type. The same research group previously reported that acid sphingomyelinaselike protein (SMPDL3A; alternatively called ASML3a) is upregulated by DBC1 (Wright et al, 2002).…”