Greg Sowa , Ph.D.

Assistant Professor SowaG@missouri.edu

Research Interests
The long term goal of my research is better understanding the molecular and cellular aspects of the function of proteins associated with detergent resistant membranes (DRMs).
DRMs are operationally defined based on their insolubility in such mild detergents as Triton X-100 and ability to float in sucrose gradients due to their low buoyant density. DRMs can be divided into two major entities, i.e., lipid rafts and caveolae (60-100nm diameter), which are noncoated flask-shaped invaginations of plasma membrane abundant in proteins called caveolins. Caveolin-1 and -2 are primary focus of my current research.
In the past, we have determined that formation of morphologically defined caveolae is necessary for caveolin-1 to inhibit endothelial nitric oxide synthase (eNOS) activity in intact cells (Sowa et al., 2001).
As a follow up study we have established that in human prostate cancer cells, in which caveolin-1 alone failed to form plasma membrane caveolae, co-expression of caveolin-2 allowed for these organelles to form. Furthermore, we have also determined that serine phosphorylation of caveolin-2 appeared to be an important molecular mechanism via which caveolin-2 facilitates formation of fully invaginated caveolae in the presence of caveolin-1 (Sowa et al., 2003).

Presently, there are 2 major research directions explored in my laboratory:
i. The role of DRMs in regulating endothelial cell function
ii. Te role of DRMs in regulating cancer growth and progression

i. In regard to the first direction, which is partially funded by American Heart Association, we look at the role of caveolins in regulating endothelial cell signaling and function. Our current focus is regulation of caveolin-2 phosphorylation and its role in endothelial cell function. So far, we have confirmed that serine phosphorylation of caveolin-2 also occurs in endothelial cells and is modulated by caveolin-1 as well as by targeting to DRMs (Sowa et al., in preparation).
Interestingly, the lungs of genetically engineered mice lacking caveolins are not fully functional, resulting in exercise intolerance. The major reason for this malfunction in caveolin knockout mice is that the responsible for gas exchange alveolar septa is thickened due to hypercellularity involving an increased number of endothelial cells. The cause of this hypercellularity is unknown but strongly suggests that caveolins may be involved in maintaining a fine balance between endothelial cell proliferation and differentiation, and possibly apoptosis (a programmed cell death). Likely changes in endothelial cell migration/adhesion can also be considered to play a role. All the above mentioned processes are crucial for angiogenesis (new blood vessel formation and maintenance). Therefore, by overexpressing or knocking down caveolins with small interfering RNA (siRNA), were are currently testing the relative involvement of caveolin-1 and -2 in regulating pertinent to angiogenesis endothelial functions and signaling. Concurrent to our functional studies, we are also applying both qualitative and quantitative approaches to determine how caveolins affect the protein composition of DRMs isolated from the lung tissues of wild type and caveolin knockout mice.

ii. The major rational behind our second research area are multiple basic and clinical research data suggesting a strong correlation between expression of either caveolin-1 or -2 and cancer progression. Caveolin-1 is believed to be a tumor suppressor protein, which was confirmed by studies of several independent groups overexpressing caveolin-1 in cultured cancer cells. In vivo data suggest a more complex role for caveolin-1 in cancer. Similar to observations in cancer cells, most data obtained in animals point towards tumor growth suppression by caveolin-1, however, there are also studies implying that caveolin-1 may play a positive role in later phases of tumor progression. Surprisingly, there is no basic research data on the specific role of the major interacting partner for caveolin-1, i.e., caveolin-2 in cancer. To clearly reconcile these often contradictory observations and to determine the specific role of caveolins in cancer, more comprehensive studies focusing on selective targeting of caveolin-1, -2 or both are needed. To meet these needs, using siRNA expressed in retroviral systems, we were able to stably knock down caveolin-1 and -2 in human lung adenocarcinoma cell line A549 at both mRNA and protein levels and are in a process of testing tumorigenic properties of these stable populations of A549 in cell based assays as well as in immunocompromised mice.

Professional Background

• Sowa G., Liu J., Papapetropoulos A., Rex-Haffner M., Hughes TE., and Sessa WC. Trafficking of Endothelial Nitric-oxide Synthase in Living Cells. QUANTITATIVE EVIDENCE SUPPORTING THE ROLE OF PALMITOYLATION AS A KINETIC TRAPPING MECHANISM LIMITING MEMBRANE DIFFUSION. Journal of Biological Chemistry 1999, 274: 22524-22531.
• Morales-Ruiz M, Fulton D, Sowa G, Languino LR, Fujio Y, Walsh K, Sessa WC. Vascular endothelial growth factor-stimulated actin reorganization and migration of endothelial cells is regulated via the serine/threonine kinase Akt. Circulation Research 2000, Apr 28; 86(8): 892-6.
• Paxinou E, Weisse M, Chen Q, Souza JM, Hertkorn C, Selak M, Daikhin Eyudkoff M, Sowa G, Sessa WC, Ischiropoulos H. Dynamic regulation of metabolism and respiration by endogenously produced nitric oxide protects against oxidative stress. Proc Natl Acad Sci USA 2001, 98(20): 11575-80.
• Sowa G, Pypaert M, Sessa WC. Distinction between signaling mechanisms in lipid rafts versus caveolae. Proc Natl Acad Sci USA 2001, 98(24): 14072-77.
• Fulton D, Fontana J, Sowa G, Gratton JP, Li KX, Michell B, Kemp BE, Rodman D, Sessa WC. Localization of Akt phosphorylated endothelial nitric oxide synthase and nitric oxide in Golgi and plasma membrane defines the existence of two pools of active enzyme. Journal of Biological Chemistry 2002, 277: 4277-84.
• Sowa G, Pypaert M, Fulton D, Sessa WC. The phosphorylation of caveolin-2 on serines 23 and 36 modulates caveolin-1 dependent caveolae formation. Proc Natl Acad Sci USA 2003, 100(11):6511-6.
• Peterson1 TE, Abe JI, Kleppe1 LS, Mueske CS, Mookadam M, Chen L, Sowa G, Sessa WC and Simari RD. Caveolin-1 is a target and a modulator of PDGF signaling in vascular smooth muscle cells. Arterioscler Thromb Vasc Biol. 2003, 23(9): 1521-7.
  

Methodology/Techniques
Molecular Biology
Cell Culture
Cell Biology
Cell Pharmacology
Proteomics
Biochemistry
Laboratory Mouse