Fhit loss in lung preneoplasia: relation to DNA damage response checkpoint activation

Abstract

Loss of heterozygosity at the FHIT locus is coincident with activation of DNA damage response checkpoint proteins; thus damage at fragile loci may trigger checkpoint activation. We examined preneoplastic lesions adjacent to non-small cell lung carcinomas for alterations to expression of Fhit and activated checkpoint proteins. Expression scores were analyzed for pair-wise associations and correlations among proteins and type of lesion. Hyperplastic and dysplastic lesions were positive for nuclear gammaH2AX expression; 12/20 dysplastic lesions were negative for Fhit expression. Fhit positive lesions showed expression of most checkpoint proteins examined, while Fhit negative lesions showed absence of expression of Chk1 and phosphoChk1. The results show that loss of expression of Fhit is significantly directly correlated with absence of activated Chk1 in dysplasia, and suggest a connection between loss of Fhit and modulation of checkpoint activity.

Fig. 1

Representative micrographs illustrating expression of the DNA damage response related proteins in preneoplastic lesions adjacent to NSCLCs. Top row: normal bronchial epithelium showing strong Fhit expression, absence of DSBs or replication fork damage indicated by lack of H2AX expression and lack of expression of DNA damage response associated proteins. Second row: in a Fhit negative AAH, nuclear H2AX is expressed, demonstrating recognition of DNA damage; pChk2 is also expressed, indicating activation of the ATM/Chk2 checkpoint pathway, and 53BP1 is expressd in nuclear foci. Third row: A Fhit positive AAH showing activation of the ATM/Chk2 and the Chk1 pathways, as well as nuclear foci of 53BP1. Fourth row: A Fhit negative DH with H2AX expression and abortive activation of the ATM pathway, lacking evidence of Chk2 or Chk1 activation and showing only an occasional cell with 53BP1 foci. Fifth row: A Fhit negative DL showing evidence of activation of the ATM/Chk2 pathway but not the Chk1 checkpoint, and some cells with large 53BP1 foci.

Fig. 2

Hypothetical sequence of molecular events in progression of high grade lung dysplasia.