Functional and Structural Aspects of La Protein Overexpression in Lung Cancer

Purpose p53 and RAS are multifunctional proteins that are critical to cell cycle regulation, apoptosis, cell survival, gene transcription, response to stress, and DNA repair. We have evaluated the prognostic and predictive value of p53 gene/protein aberrations using tumor samples from JBR.10, a North American phase III intergroup trial that randomly assigned 482 patients with completely resected stage IB and II non–small-cell lung cancer (NSCLC) to receive four cycles of adjuvant cisplatin plus vinorelbine or observation alone. Methods p53 protein expression was evaluated by immunohistochemistry. Mutations in exons 5 to 9 of the p53 gene were determined by denaturing high-performance liquid chromatography and confirmed by sequencing. RAS mutations were identified by allelic specific oligonucleotide hybridization. Results Of 253 patients, 132 (52%) were positive for p53 protein overexpression. Untreated p53-positive patients had significantly shorter overall survival than did patients with p53-negative tumors (hazard ratio [HR] = 1.89; 95% CI, 1.07 to 3.34; P = .03). However, these p53-positive patients also had a significantly greater survival benefit from adjuvant chemotherapy (HR = 0.54; P = .02) compared with patients with p53-negative tumors (HR = 1.40; P = .26; interaction P = .02). Mutations of p53 and RAS genes were found in 124 (31%) of 397 and 117 (26%) of 450 patients, respectively. Mutations in these genes were neither prognostic for survival nor predictive of a differential benefit from adjuvant chemotherapy. Conclusion p53 protein overexpression is a significant prognostic marker of shortened survival, and also a significant predictive marker for a differentially greater benefit from adjuvant chemotherapy in completely resected NSCLC patients.

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The Cellular Protein La Functions in Enhancement of Virus Release through Lipid Rafts Facilitated by Murine Leukemia Virus Glycosylated Gag

mBio ◽

10.1128/mbio.00341-10 ◽

2011 ◽

Vol 2 (1) ◽

Cited By ~ 4

Author(s):

Takayuki Nitta ◽

Raymond Tam ◽

Jung Woo Kim ◽

Hung Fan

Keyword(s):

Lipid Rafts ◽

Cellular Protein ◽

Cellular Proteins ◽

Virus Release ◽

Protein Overexpression ◽

Particle Release ◽

La Protein ◽

Leukemia Viruses ◽

Hiv 1 ◽

Murine Leukemia

ABSTRACTMurine leukemia viruses (MuLVs) encode two forms of Gag polyprotein: the precursor for the viral core proteins (Pr65gagfor Moloney MuLV [M-MuLV]) and a longer glycosylated form (glyco-gag, or gPr80gag). gPr80gagis translated from the same unspliced viral RNA as Pr65gag, from an upstream in-frame CUG initiation codon. As a result, gPr80gagcontains 88 unique N-terminal amino acids that include a signal peptide that conducts gPr80gaginto the rough endoplasmic reticulum, where it is glycosylated, exported to the cell surface, and cleaved into two proteins of 55 and 40 kDa. The amino-terminal 55-kDa protein remains cell associated with the 88 unique amino acids exposed to the cytosol. We previously showed that gPr80gagfacilitates efficient M-MuLV release through lipid rafts. In this report, we found that the unique N-terminal domain of gPr80gagis sufficient to facilitate enhanced M-MuLV particle release from transfected 293T cells. A search for cellular proteins involved in gPr80gagfunction led to cellular La protein. Overexpression of mouse or human La enhanced M-MuLV particle release in the absence of glyco-gag, and the released virus had a reduced buoyant density characteristic of increased cholesterol content. Moreover, small interfering RNA (siRNA) knockdown of human La abolished glyco-gag enhancement of M-MuLV release. These results implicate La as a cellular protein involved in M-MuLV glyco-gag function. We also found that overexpression of mouse or human La could enhance HIV-1 release in the absence of gPr80gag. Therefore, M-MuLV and HIV-1 may share a pathway for release through lipid rafts involving La.IMPORTANCERetroviruses cause diseases such as leukemia and AIDS. An important aspect of viral replication is how viruses are released from infected cells. We previously found that a unique protein encoded by murine leukemia viruses (MuLVs), glyco-gag (or gPr80gag), enhances efficient virus release through cholesterol-rich membrane subdomains called lipid rafts. In this study, we found that the N-terminal domain of gPr80gagis sufficient to enhance viral release. A search for cellular proteins that participate in gPr80gagfunction led to cellular La protein. Overexpression of La phenocopied glyco-gag in enhancing M-MuLV release, and knockdown of La abolished glyco-gag function. M-MuLV glyco-gag also enhanced release of HIV-1, as did overexpression La in the absence of glyco-gag. Thus, M-MuLV and HIV-1 may share a cellular pathway for release through lipid rafts involving La. These results may also be relevant for other viruses that are released through lipid rafts.

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