Hypoxia up-regulates expression of hemoglobin in alveolar epithelial cells.
Alveolar epithelial cells are directly exposed to acute and chronic fluctuations in alveolar oxygen tension. Previously, we found that the oxygen-binding protein hemoglobin is expressed in alveolar Type II cells (ATII). Here, we report that ATII cells also express a number of highly specific transcription factors and other genes normally associated with hemoglobin biosynthesis in erythroid precursors. Because hypoxia-inducible factors (HIFs) were shown to play a role in hypoxia-induced changes in ATII homeostasis, we hypothesized that the hypoxia-induced increase in intracellular HIF exerts a concomitant effect on ATII hemoglobin expression. Treatment of cells from the ATII-like immortalized mouse lung epithelial cell line-15 (MLE-15) with hypoxia for 20 hours resulted in dramatic increases in cellular levels of HIF-2α protein and parallel significant increases in hemoglobin messenger RNA (mRNA) and protein expression, as compared with that of control cells cultured in normoxia. Significant increases in the mRNA of globin-associated transcription factors were also observed, and RNA interference (RNAi) experiments demonstrated that the expression of hemoglobin is at least partially dependent on the cellular levels of globin-associated transcription factor isoform 1 (GATA-1). Conversely, levels of prosurfactant proteins B and C significantly decreased in the same cells after exposure to hypoxia. The treatment of MLE-15 cells cultured in normoxia with prolyl 4-hydroxylase inhibitors, which mimic the effects of hypoxia, resulted in increases of hemoglobin and decreases of surfactant proteins. Taken together, these results suggest a relationship between hypoxia, HIFs, and the expression of hemoglobin, and imply that hemoglobin may be involved in the oxygen-sensing pathway in alveolar epithelial cells.
Grek
Christina L
CL
Department of Pediatrics and Neonatology, Medical University of South Carolina, Charleston, SC 29425, USA. baatzje@musc.edu
Newton
Danforth A
DA
Spyropoulos
Demetri D
DD
Baatz
John E
JE
D056809:Alveolar Epithelial Cells / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D000818:Animals; D015687:Cell Hypoxia / Q000235:genetics; D002460:Cell Line; D004791:Enzyme Inhibitors / Q000494:pharmacology; D041905:Erythroid Cells / Q000187:drug effects / Q000378:metabolism; D050982:GATA1 Transcription Factor / Q000235:genetics / Q000378:metabolism; D006418:Heme / Q000378:metabolism; D006454:Hemoglobins / Q000235:genetics* / Q000378:metabolism; D000860:Hypoxia / Q000235:genetics*; D007150:Immunohistochemistry; D051379:Mice; D011393:Procollagen-Proline Dioxygenase / Q000037:antagonists & inhibitors / Q000378:metabolism; D037721:Pulmonary Surfactant-Associated Protein C / Q000235:genetics / Q000378:metabolism; D015854:Up-Regulation / Q000187:drug effects / Q000235:genetics*
D004791:Enzyme Inhibitors; D050982:GATA1 Transcription Factor; D006454:Hemoglobins; D037721:Pulmonary Surfactant-Associated Protein C; D006418:Heme; D011393:Procollagen-Proline Dioxygenase