Aberrant splicing of the TSG101 and FHIT genes occurs frequently in multiple malignancies and in normal tissues and mimics alterations previously described in tumours

Abstract

Intragenic deletions of TSG101, the human homolog of a mouse gene (tsg101) that acts to suppress malignant cell growth, were reported in human breast tumours. We screened TSG101 for somatic mutations in DNA and RNA samples isolated from a variety of common human malignancies, EBV-immortalised B-cells, and normal lung parenchyma. Intragenic TSG101 deletions in RNA transcripts were frequently found in all types of samples. Analysis of DNA failed to show genomic rearrangements corresponding to transcripts containing deletions in the same samples. The breakpoints of most transcript deletions coincide with genuine or cryptic splice site sequences, suggesting that they result from alternative or aberrant splicing. A similar spectrum of transcript deletions has previously been described in the putative tumour suppressor gene FHIT. We analysed FHIT in the same series of RNA samples and detected truncated FHIT transcripts frequently in both tumour and normal tissues. In addition, transcripts from TSG101, FHIT and seven other genes were analysed in RNA isolated from normal peripheral blood lymphocytes. Large TSG101 and FHIT intragenic transcript deletions were detected and these appeared to be the predominant transcript iǹ aged' lymphocytes. Similar alterations were not detected in transcripts of the other genes which were analysed. Our ®ndings demonstrate that truncated TSG101 and FHIT transcripts are commonly detected in both normal and malignant tissues and that a signi®cant fraction of these are likely to be the result of aberrant splicing. While we cannot exclude that alterations in TSG101 and FHIT occur during cancer development, our data indicate that in this context the commonly observed transcript abnormalities are misleading.

Expression of a new isoform of the tumor susceptibility TSG101 protein lacking a leucine zipper domain in Burkitt lymphoma cell lines

“…From the perspective of tumor biology, the removal of this control point will permit the expansion of the tumor cell population. This is consistent with the observation of an increase in aberrant TSG101 transcripts in carcinoma cells when compared to normal cells (Gayther et al, 1997;Lin et al, 1998). Other proteins, such as transcription factor NF-kB and retinoblastoma, can also be regulated by ubiquitination.…”

“…Most of the TSG101 deletions detected in BL and resulting in non coding transcripts are similar to those reported in breast (Lee and Feinberg, 1997;Li et al, 1997;Steiner et al, 1997), prostate carcinomas (Sun et al, 1997), small cell lung carcinoma (Oh et al, 1998) and acute myeloid leukemia (Lin et al, 1998). These splicing aberrations can also be detected in normal cells although at a much lower frequency, suggesting there is a biological selection for them in tumor cells (Gayther et al, 1997;Oh et al, 1998). Among these, the joining of nucleotides 153 ± 1055 represents the most common and abundant aberrant transcript in all types of tumors breast (Lee and Feinberg, 1997;Li et al, 1997;Lin et al, 1998;Oh et al, 1998;Steiner et al, 1997;Sun et al, 1997).…”

“…Normal TSG101 protein can be detected with antibodies in breast carcinoma cell lines (Zhong et al, 1997). These aberrant messages are always coexpressed with a normal transcript in tumor cells (Lee and Feinberg, 1997), and they are also detectable, albeit at a much lower frequency, in normal cells (Gayther et al, 1997;Lin et al, 1998). So far there is no evidence that any of these alternatively spliced TSG101 messages can code for a protein, despite the fact that alternative splicing is a well known mechanism in the generation of variant forms of a protein in cell di erentiation and development.…”

HYAL1LUCA-1, a candidate tumor suppressor gene on chromosome 3p21.3, is inactivated in head and neck squamous cell carcinomas by aberrant splicing of pre-mRNA

“…The sex-lethal autoregulatory circuit in drosophila is one such model where 5' UTR splice variants regulate gene expression (Granadino et al, 1997). Aberrant or alternative splicing of other candidate tumor suppressor genes such as FHIT and TSG101 have been reported, and generally appear to be epigenetic rather than mutations at intron-exon boundaries (Gayther et al, 1997).…”

Frequent allelic deletion at the FHIT locus associated with p53 overexpression in squamous cell carcinoma subtype of Taiwanese non-small-cell lung cancers

“…Whereas LOH is generally associated with decreased protein expression, protein inactivation may be due to complex mechanisms other than deletion within an allele (Tanaka et al, 1998). Alternatively, abnormal protein expression may occur in the absence of genetic alterations through altered splicing fidelity (Gayther et al, 1997). Besides, methylation of FHIT is another important mechanism for loss of Fhit expression (Zöchbauer-Müller et al, 2001).…”