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Neoplastic transformation and tumorigenesis associated with sam68 protein deficiency in cultured murine fibroblasts
K Liu1, L Li, P E Nisson
1Department of Genetics and Department of Medicine, Stanford University School of Medicine, Stanford, California 94305-5120, USA.
Abstract:
Sam68 is a multimeric 68-kDa RNA-binding nuclear protein of unknown function that interacts with, and is tyrosine-phosphorylated by, the oncogenic protein Src during mitosis. Random homozygous knock-out (RHKO) is a retroviral-based antisense RNA strategy that can identify chromosomal genes whose functional disablement leads to reversible tumorigenic capabilities. Here we report that RHKO-induced Sam68 deficiency results in neoplastic transformation of murine NIH3T3 fibroblasts. Whereas simple haploinsufficiency of Sam68 produced by insertion mutagenesis in a single chromosomal allele did not detectably affect cell growth, reduction of Sam68 protein to <25% of the wild type level was associated with anchorage-independent growth, defective contact inhibition, and the ability to form metastatic tumors in nude mice. These properties were reversed by cessation of RHKO inactivation. Our findings, which indicate that the Sam68 protein level can prominently affect cell proliferation, implicate Sam68 function in tumorigenesis. Consistent with these results is evidence that cells undergoing mitosis show a dramatic reduction in the level of Sam68 protein.
Insights
Sam68 deficiency causes neoplastic transformation, leading to anchorage-independent growth and tumor formation. Reducing Sam68 protein levels impacts cell proliferation and tumorigenesis, with effects reversible upon RHKO inactivation.
Area of Science:
- Molecular Biology
- Oncology
- Cell Biology
Background:
- Sam68 is a nuclear protein interacting with the oncogenic Src protein during mitosis.
- The function of Sam68 remains largely unknown.
- Random homozygous knock-out (RHKO) is a retroviral strategy to identify genes involved in tumorigenesis.
Purpose of the Study:
- To investigate the role of Sam68 in neoplastic transformation.
- To determine the effect of Sam68 deficiency on cell proliferation and tumorigenic capabilities.
Main Methods:
- Utilized RHKO strategy to induce Sam68 deficiency in murine NIH3T3 fibroblasts.
- Assessed anchorage-independent growth, contact inhibition, and tumor formation in nude mice.
- Observed reversibility of neoplastic properties upon RHKO inactivation.
Main Results:
- RHKO-induced Sam68 deficiency led to neoplastic transformation of NIH3T3 fibroblasts.
- Significant reduction of Sam68 protein (<25% wild type) caused anchorage-independent growth and defective contact inhibition.
- Tumorigenic properties were reversed when RHKO inactivation ceased.
- Mitotic cells exhibited a dramatic reduction in Sam68 protein levels.
Conclusions:
- Sam68 protein levels significantly influence cell proliferation.
- Sam68 plays a crucial role in tumorigenesis.
- The findings implicate Sam68 as a potential target in cancer research.
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