Tsg101 Is Essential for Cell Growth, Proliferation, and Cell Survival of Embryonic and Adult Tissues

Abstract

Tumor susceptibility gene 101 (Tsg101) was identified in a random mutagenesis screen for potential tumor suppressors in NIH 3T3 cells. Altered transcripts of this gene have been detected in sporadic breast cancers and many other human malignancies. However, the involvement of this gene in neoplastic transformation and tumorigenesis is still elusive. Using gene targeting, we generated genetically engineered mice with a floxed allele of Tsg101. We investigated essential functions of this gene in vivo and examined whether the loss of function of Tsg101 results in tumorigenesis. Conventional knockout mice were generated through Cre-mediated excision of the first coding exon in the germ line of mouse mammary tumor virus (MMTV)-Cre transgenic mice. The complete ablation of Tsg101 in the developing embryo resulted in death around implantation. In contrast, mammary gland-specific knockout mice developed normally but were unable to nurse their young as a result of impaired mammogenesis during late pregnancy. Neither heterozygous null mutants nor somatic knockout mice developed mammary tumors after a latency of 2 years. The Cre-mediated deletion of Tsg101 in primary cells demonstrated that this gene is essential for the growth, proliferation, and survival of mammary epithelial cells. In summary, our results suggest that Tsg101 is required for normal cell function of embryonic and adult tissues but that this gene is not a tumor suppressor for sporadic forms of breast cancer.

Parity-induced mammary epithelial cells facilitate tumorigenesis in MMTV-neu transgenic mice

“…The conditional knockout of the tumor susceptibility gene 101 (Tsg101) causes cell cycle arrest and cell death in vitro and in vivo (Krempler et al, 2002;Wagner et al, 2003). Tsg101 is, however, not a tumor suppressor gene as previously reported.…”

“…On the contrary, we can demonstrate that this gene is indispensable for the survival of normal, immortalized, and fully transformed cell lines (Carstens et al, 2004, submitted). The Wap-Cre-mediated deletion of this gene impaired mammary lobulogenesis during pregnancy and lactation due to increased cell death (Wagner et al, 2003). According to our experimental design, the Wap-Cre-mediated deletion of Tsg101 should therefore significantly reduce the number of untransformed, hormone-responsive cells that are the proposed cellular targets for the neoplastic transformation in MMTV-neu mice.…”

“…One primary tumor was X-gal negative, which might suggest that this lesion had a different cellular origin. It is, however, more reasonable to propose that these cells are the progeny of PI-MECs that lack activation of the Wap promoter due to the mosaic expression pattern of Wap-Cre transgene, which was reported previously (Wagner et al, 2003). Three animals with X-gal-positive mammary tumors were examined for pulmonary metastasis to determine whether transformed PI-MECs are capable of spreading to distant sites.…”

The Human Endosomal Sorting Complex Required for Transport (ESCRT-I) and Its Role in HIV-1 Budding

“…Although the protein has not been shown defini-tively to act as a tumor suppressor in vivo, its expression is reduced in human cellular carcinomas, and reduction of VPS37A/HCRP1 levels in the human cellular carcinoma cell line BEL-7404 stimulates cell growth and enhances cell invasiveness in vitro (39). Similarly, reductions of TSG101 levels allowed NIH3T3 cells to grow on soft agar and to form metastatic tumors in nude mice (65), although genetic deletions of TSG101 do not induce tumor formation (66). It therefore appears that altered levels (or composition) of ESCRT-I can give rise to improperly regulated cell growth in some contexts.…”

S14 as a Therapeutic Target in Breast Cancer

“…We predict that a complete mammary-specific knockout will not be lethal, and that it will permit the flexibility to analyze S14 function in selected mammary epithelial subtypes or in pregnancy-dependent models using appropriate Cre-expressing mice (52). To this end we produced mice with germline transmission of a floxed S14 allele (not shown), and will use them in conjunction with mice harboring transgenes for both mammary epithelial Cre recombinase expression and a mammary oncogene.…”