Department of Medicine
University of Pittsburgh
Rama K. Mallampalli, MD
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Professor of Medicine Phone: 412-6247-8735 |
Bio
Dr. Mallampalli received his MD from the University of Wisconsin. He completed an internship and residency in Internal Medicine at Hennepin County Medical Center in Minneapolis, MN where he also served as chief medical resident. Dr. Mallampalli completed a Pulmonary and Critical Care fellowship at the University of Iowa, where he obtained his research training under the mentorship of Dr. Gary Hunninghake. At Iowa, Dr. Mallampalli was appointed Professor of Medicine and Biochemistry and served as Associate Chair. Dr. Mallampalli serves as Editor for the Journal of Biological Chemistry and the American Journal of Physiology. He serves on multiple peer review panels including the LIRR Study Section for NIH grant reviews. He is an elected member of the American Society of Clinical Investigation, an Established Investigator of the American Heart Association, and a Career Investigator of the American Lung Association. In September of 2009, Dr. Mallampalli was recruited as Chief of the Pulmonary Division of the VA Pittsburgh Healthcare System and as the Director of the Acute Lung Injury Center at the University of Pittsburgh.
Academic and Research Interests
Dr. Mallampalli’s research in the area pulmonary epithelial molecular and cell biology as it relates to acute lung injury and the mechanisms of sepsis. He is a nationally recognized investigator in the area of pulmonary lipid metabolism.
The primary goal of his research is to investigate the molecular mechanisms for control of the major phospholipid of animal membranes and of lung surfactant, phosphatidylcholine (PC). PC levels are tightly controlled, in part, by the rate-regulatory phosphoenzyme cytidylyltransferase (CCT). His work investigates the molecular physiology of how CCT is controlled by reversible phosphorylation events within its carboxyl-terminus and its regulation by enzyme turnover. In models of inflammatory lung injury, surfactant PC biosynthesis is impaired because CCT activity decreases as a result of post-translational enzyme modification and gene transcriptional repression. Specifically, he has discovered that CCT is coordinately degraded by calpains and the ubiquitin system in models of pulmonary sepsis. These adverse effects are opposed by the calcium- sensor, calmodulin, that binds and stabilizes CCT during infection. CCT is also inactivated by stress kinases stimulated during lung inflammation that target novel docking motifs and phosphorylation sites within the enzyme resulting in greatly decreased PC production.
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Figure 1. Calmodulin (CaM) Binds CCTα In Vivo. A. Mammalian 2-hybrid assay. Cells were co-transfected with CCTα-Gal4BD (CCTα) and CaM-Gal4AD (CaM) plasmids as fusion proteins separately [inset] or in combination with a plasmid construct encoding a b-galactosidase reporter gene (pG5CAT). Cells were lysed and assayed for b-galactosidase activities. B. FRET Analysis. Cells were transfected with YFP-CaM and CFP-CCTα and CaM-CCTα interaction at the single cell level was imaged using laser scanning microscopy before and after photobleaching. Shown in the upper sets of panels is single cell imaging showing that after acceptor photobleaching, fluorescence intensity of YFP decreased and CFP increased, confirming protein interaction between CaM and CCTα. Below: the same FRET was confirmed quantitatively by graphing of fluorescence intensities.
Dr. Mallampalli’s second area of research interest is in the molecular control of ubiquitin E3 ligases and how they might impact lipogenic proteins. His current activity investigates how calcium-regulated effectors control site-specific ubiquitination of target lung proteins (e.g. CCT) that in turn ultimately increase degradation of these substrates through proteasome-independent sorting. Dr. Mallampalli uses gene transfer approaches to express new CCT mutant enzymes in alveolar epithelia that are resistant to proteolysis and phosphorylation events thereby restoring surfactant PC to high levels in alveolar injury.
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Figure 2. A model for CCTα nuclear activation, exclusion, and proteolytic processing mediated by protein monoubiquitination. A. Schematic diagram illustrating proposed pathways by which CCTα is regulated by monoubiquitination. (1) CCTα monoubiquitination at K57 leads to masking of its NLS, thus mislocalizing the enzyme to the lysosome for degradation. (2) Under conditions when demand for PtdCho synthesis is high, editing of monoubiquitinated CCTα by the action of deubiquitinating enzymes (DUBs) may result in free CCTα. Deubiquitinated CCTα can either (3) dock to ER membranes or (4) translocate to the nuclear envelope by NLS-directed recruitment of karyopherins, such as importin-a (Ia) to augment PtdCho synthesis. Last, when demand for membrane phospholipid synthesis is low, nuclear CCTα can undergo monoubiquitination and export for proteolytic processing via the lysosomal pathway outlined in this study.
Fig. 3. The E3 Ligase, SCF. Cartoon showing key domains of F-Box containing E3 ligases. By using adaptor subunits, Skp1 and Cullin, the F-Box serves as a platform to bring an 8.5 kDa ubiquitin moiety (red) linked to the E2 ubiquitin-conjugating (Ubc) enzyme within close intermolecular distance to its target substrate, e.g. CCT. The substrate CCT binds within a WD/LRR motif in the C-terminal end of F-box whereas Skp1 binds within the F-Box Motif. Also shown is a C-terminal CAAX sequence (geranyl-geranyl, [GG]) involved in anchoring the E3 ligase to membranes. Once Skp1 and CCT dock within F-Box, the E2 (Ubc) ligase catalyzes transfer of ubiquitin to CCT thereby branding it for degradation.
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Key Publications
Chen BB, Glasser JR, Coon TA, and Mallampalli RK. F box protein FBXL2 exerts human lung tumor suppressor-like activity by ubiquitin-mediated degradation of cyclin D3 resulting in cell cycle arrest. Oncogene, 31: 2566-2579, 2012.
Agassandian M, Chen BB, Pulijala R, and Mallampalli RK. Calcium-calmodulin kinase I cooperatively regulates nucleocytoplasmic shuttling of CCTα by accessing a nuclear export signal. Mol. Biol. Cell (In Press), 2012.
Chen BB, Glasser JR, Coon TA, Zou C, Miller HL, Fenton, M, McDyer JF, Boyiadzis M, and Mallampalli RK. F box protein FBXL2 targets cyclin D2 for ubiquitination and degradation to inhibit leukemic cell proliferation. Blood 119 (13): 3132-3141, 2012, 2012.
Zhao J, Wei J, Mialki RK, Chen BB, Coon C, Zou C, *Mallampalli RK, Zhao Y. F-box protein FBXL19-mediated ubiquitination and degradation of the IL-33 receptor limits pulmonary inflammation. Nat. Immunol. (In Press), 2012. *co-senior author.
Chen BB, Coon TA, Glasser JR, and Mallampalli RK. Calmodulin antagonizes a calcium-activated SCF ubiquitin E3 ligase subunit, FBXL2, to regulate surfactant homeostasis. Mol. Cell. Biol. 31: 1905-1920, 2011.
Ray NB, Durairaj L, Chen BB, McVerry BJ, Ryan AJ, Donahoe M, Waltenbaugh AK, O'Donnell CP, Henderson FC, Etscheidt C, McCoy D, Agassandian M, Hayes-Rowan E, Coon TA, Butler TL, Gakhar L, Mathur SN, Sieren JC, Tyurina YY, Kagan VE, McLennan G, and Mallampalli RK. Dynamic regulation of cardiolipin by the lipid pump, ATP8b1, determines the severity of lung injury in experimental pneumonia. Nat. Med. 16:1120-27, 2010.
PubMed Link
News
Read Dr. Mallampalli's recent article in Nature Medicine.