Proliferation, C- myc, and cyclin D1 expression in diffuse alveolar damage: potential roles in pathogenesis and implications for prognosis

Abstract

In this study, we compared expression of DNA topoisomerase IIα, a marker of cellular proliferation, c- myc, and cyclin D1 in lung biopsy specimens showing diffuse alveolar damage (DAD) with control lung tissues. We subsequently correlated DNA topoisomerase IIα, c- myc, and cyclin D1 expression with survival. We hypothesized that poor outcome may correlate with a higher proliferation index, and that c- myc and cyclin D1 activation are potentially important regulators of both proliferation and apoptosis in DAD. Immunohistochemical stains for c- myc, cyclin D1, and DNA topoisomerase IIα were performed on 10 cases of DAD (15 cases for DNA topoisomerase IIα) and 10 control lungs. A proliferation index for each case was calculated by dividing the number of nuclei expressing DNA topoisomerase IIα by the total number of nuclei counted. The percentages of alveolar pneumocytes and interstitial cells staining positively for c- myc and cyclin D1 were estimated. The average proliferation index (DNA topoisomerase IIα index) in DAD (0.16 ± 0.06, n = 15) was significantly greater than in control lungs (0.00 ± 0.01, n = 10) ( P < .0001). The average proliferation index of patients with DAD who died of respiratory failure (0.18 ± 0.05, n = 9) was significantly greater than the average proliferation index of patients whose respiratory disease resolved or stabilized (0.11 ± 0.05, n = 5) ( P < .03). Expression of c- myc in alveolar pneumocytes and interstitial cells was more intense and slightly more widespread in cases of DAD compared with control lungs. In 9 of 10 cases of DAD, cyclin D1 expression was present in up to 30% of alveolar pneumocytes and up to 10% of interstitial cells. No staining for cyclin D1 was present in control lungs. These results show that the proliferation index in DAD potentially correlates with patient survival. Furthermore, enhanced expression of c- myc and cyclin D1 may contribute to dysregulation of cellular proliferation and apoptosis observed in DAD.