Dr. Joseph L. Alcorn

Department of Pediatrics, Division of Neonatal-Perinatal Medicine
Program in Biochemistry and Molecular Biology

University of Texas-Houston Medical School
P.O. Box 20708 - Houston, Texas 77225
(713) 500-5641: fax (713) 500-5794
email: Joseph.L.Alcorn@uth.tmc.edu

Ph.D., University of Texas at Dallas
Postdoctoral Research: University of Texas Southwestern Medical Center at Dallas

Molecular Mechanisms Involved in the Regulation of Pulmonary Surfactant Protein Gene Expression by Hormones

Pulmonary surfactant is a lipoprotein complex produced exclusively by type II pneumonocytes of the lung alveolus and acts to reduce surface tension at the air/liquid interface. Expression of surfactant is developmentally regulated and is enhanced by the presence of hormones, such as glucocorticoids. Prematurely born infants in which of synthesis of surfactant is not initiated or is reduced are prone to develop Respiratory Distress Syndrome (RDS), the leading cause of neonatal morbidity and mortality in developed countries.

Research in my laboratory is focused on the molecular mechanisms whereby steroid hormones modulate pulmonary surfactant gene expression in type II pneumonocytes. I have chosen to study the post-transcriptional regulation of pulmonary surfactant protein A (SP-A) mRNA and pulmonary surfactant protein B (SP-B) mRNA and the transcriptional regulation of the pulmonary surfactant protein C (SP-C) gene by glucocorticoids in human type II pneumonocytes. Glucocorticoids act to increase the rate of transcription of the human SP-A, SP-B, and SP-C genes. However, glucocorticoids also act post-transcriptionally to affect SP-A and SP-B levels in human lung. Glucocorticoids act to decrease the stability of SP-A mRNA and to increase the stability of SP-B mRNA. SP-A and SP-B expression occurs in type II pneumonocytes and bronchiolar Clara cells and is initiated later in gestation. We use isolated type II cells in primary culture transfected with recombinant adenoviruses carrying fusions of the surfactant genes and promoters with reporter genes to delineate the DNA and RNA sequences involved in the regulation of the genes by glucocorticoids. From these studies, we use various in vitro techniques to identify the proteins involved in the regulatory mechanisms.

The long-term goal of this research is to define molecular mechanisms whereby glucocorticoids regulate surfactant protein gene expression during fetal lung development. Identification of sequences and proteins involved in regulation of surfactant proteins and characterization of the protein interactions that mediate these effects will help define the complex mechanisms whereby glucocorticoids regulate eukaryotic gene expression.

Effects of Bt₂cAMP and dexamethasone on the levels of SP-A, SP-B and
SP-C mRNA in type II pneumonocytes in primary culture.

Type II pneumonocytes in primary culture were incubated in the absence or presence of Bt2cAMP and/or dexamethasone for 5 days. The RNA was subjected to northern analysis using radiolabeled cDNA probes specific for rabbit SP-A, SP-B or SP-C. A: Northern blot of SP_A mRNA levels in cells incubated in the absence (Con) or presence of Bt2cAMP (Bt; 1 mM). B: Northern blot of SP-A mRNA levels in cells incubated in the presence of Bt2cAMP (1 mM) (Bt), in the absence or presence of various concentrations of dexamethasone (Dex, 10-10 to 10-7 M). The position of SP-A mRNA in A and B is indicated. C: Northern blot of SP-B and SP-C mRNA isolated from type II cells incubated in the absence (Con) or presence of Bt2cAMP (1 mM), dexamethasone (10-7 M), or the two agents in combination (Bt+Dex). The positions of SP-B and SP-C mRNA in C are indicated.

Selected References

Vidaeff A, Ramin S, Gilstrap L, Alcorn JL. In vitro quantification of dexamethasone-induced SP-B expression in human lung cells. J of Maternal-Fetal Medicine. 15:155-159. 2004.

Ramin SM, Vidaeff AC, Gilstrap LC 3rd, Bishop KD, Jenkins GN Alcorn JL. The effects of dexamethasone and betamethasone on surfactant protein-B messenger RNA expression in human type II pneumocytes and human lung adenocarcinoma cells. Am J Obstet Gynecol. 190:952-959. 2004.

Alcorn, JL, Islam KN, Young PP, Mendelson CR. Glucocorticoid Inhibition of Surfactant Protein A (SP-A) Gene Expression in Lung Type II Cells is Mediated via the TTF-1 Binding Element. Am J Physiol Lung Cell Mol Physiol. 286:L767-776. 2004 .

Mustafa SB, RJ DiGeronimo, JA Petershack, JL Alcorn, and SR Seidner. Postnatal Glucocorticoids Induce a-ENaC Formation and Regulate Glucocorticoid receptors in the Preterm Rabbit Lung. Am J Physiol Lung Cell Mol Physiol. 286:L73-80. 2004.

Alcorn JL. Cell-to-cell Interactions in Lung. In Handbook of Cell Signaling, vol 2. (RA Bradshaw and EA Dennis, eds). pp 509-514, Elsevier Science, San Diego, CA, 2003.