MUTATION ANALYSIS OF THE PTEN MMAC1 GENE IN LUNG-CANCER/

We studied PTEN/MMAC1, a newly discovered candidate tumor suppressor g ene at 10q23.3, for mutations in lung cancer. One hundred and thirty-s ix lung cancer cell line DNAs (66 small cell lung cancers, SCLC, 61 no n-small cell lung cancers, NSCLC, four mesotheliomas, five extrapulmon ary small cell cancers) were analysed for PTEN/MMAC1 homozygous deleti ons and five (8%) SCLC lines showed homozygous deletions interrupting the PTEN/MMAC1 gene. Using single stranded conformation polymorphism ( SSCP) analysis, we screened the PTEN/MMAC1 open reading frame of 53 lu ng cancer cell line cDNAs for point mutations and found that 3/35 SCLC s and 3/18 NSCLCs contained homozygous amino acid sequence altering mu tations. Northern blot analysis revealed that expression of the PTEN/M MAC1 gene was considerably lower in all the tumor cell lines with poin t mutations while no expression was detected for cell lines with PTEN/ MMAC1 homozygous deletions. Mutation analysis of 22 uncultured, microd issected, primary SCLC tumors and metastases showed two silent mutatio ns, and two apparent homozygous deletions. We also discovered a proces sed pseudogene (PTEN2) which has 98.5% nt identity to PTEN/MMAC1, that needs to be accounted for in cDNA mutation analysis, Our findings sug gest that genetic abnormalities of the PTEN/MMAC1 gene are only involv ed in a relatively small subset of lung cancers.