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Department of Medicine

Department of Medicine

  Division of Pulmonary, Allergy and Critical Care Medicine



Faculty Profile: RAMA MALLAMPALLI, MD

LABORATORY LIST  |  FACULTY LIST

Dr. Mallampalli's Research

Dr. Mallampalli’s research in the area of pulmonary molecular and cell biology as it relates to acute lung injury (ALI) and the mechanisms of sepsis. He is an internationally recognized investigator in the area of lipid metabolism and ubiquitin-mediated proteolysis as it relates to inflammation and injury. His research program discovered a unique model for the molecular behavior of ubiquitin E3 ligase subunits that control inflammation. Dr. Mallampalli’s laboratory designed, synthesized, and tested the first-in-class genus of ubiquitin E3 ligase (F box) inhibitors that modulate proteolysis thereby inhibiting inflammation in preclinical models of ALI and multi-organ failure. He currently leads an NIH Program Project grant in ALI and a Centers for Advanced Diagnostics and Experimental Therapeutics in Lung Diseases Stage II (CADETII) award to develop drug therapies for inflammatory lung illness.

The primary goal of his research is to better understand inflammation, that when left unchecked, leads to tissue and organ injury. His laboratory discovered a critical role for ubiquitin E3 ligase components in the molecular control of inflammation and how they impact regulatory proteins in sepsis and pneumonia. His current activity investigates the discovery, characterization, and biological role of orphan ubiquitin E3 ligase subunits belonging to the Skp-Cullin1-F box (SCF) family that control site-specific ubiquitination and disposal of key target proteins involved in innate immunity, inflammation, and cellular lifespan.His laboratory recently discovered a new model of innate immunity that led to the synthesis of the first genus of ubiquitin E3 ligase (F box) small molecule inhibitors that modulate proteolysis thereby inhibiting inflammation in preclinical models of sepsis and multi-organ failure.

Figure 1. Molecular regulation of inflammation through pro-inflammatory cytokines mediated by F box proteins. Microbial infection or stimuli can robustly activate a variety of cell surface receptors linked to TRAF proteins that serve as critical intermediary signaling proteins to mediate cytokine synthesis and release. The F box protein Fbxl2 serves as a sentinel inhibitor of TRAFs by mediating their polyubiquitination (red circles) and proteasomal degradation in cells. Fbxl2 specifically targets at a conserved tryptophan domain within all TRAF 1-6. During microbial infection, another F box protein, Fbxo3, targets Fbxl2 for its ubiquitination and degradation at K201; this process is facilitated by glycogen synthase kinase (GSK3b) phosphorylation (green circle) of Fbxl2 at T404. Wild-type Fbxo3 in this pathway potently activates cytokine driven inflammation, whereas a naturally occurring Fbxo3V221I polymorphism is hypofunctional. A novel small molecule Fbxo3 inhibitor, BC-1215, reduces inflammation by antagonizing actions of Fbxo3 on TRAF–cytokine signaling.

 

Dr. Mallampalli’s second area of research interest is in the investigation of the mitochondrial-specific phospholipid, cardiolipin. His laboratory uncovered a new paradigm for pneumonia. Pneumonia patients had increased levels of a toxin, cardiolipin, which reproduces this disorder when given to mice. From clues in a rare disease, his group discovered that a pump normally removes cardiolipin from lung fluid but is degraded in pneumonia. These observations may be transformative in that they could lead to non-antibiotic therapies in this illness.


Figure 2. Cardiolipin, elevated in pneumonia causes lung injury.
Quantification of cardiolipin in subjects with pneumonia. A. Median (gray line) and distribution (black circles) of cardiolipin abundance in tracheal aspirates from subjects with nonpulmonary critical illness (NPCI, n = 5), pneumonia (PNA, n = 17) and CHF (n = 6). B. MicroCT scan images were obtained on live mice (in vivo) 1 h after i.t. administration of cardiolipin (50 nmol, (low), 100 nmol (high)) versus control mice (top images).

 

A third focus is to investigate the molecular mechanisms for control of major phospholipids of animal membranes and of lung surfactant, including phosphatidylcholine (PC). PC levels are tightly controlled, in part, by the rate-regulatory phosphoenzyme cytidylyltransferase (CCT). His work previously investigated 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 discovered that CCT is coordinately degraded by calpains and the ubiquitin system in models of pulmonary sepsis. However, CCT is also protected during lung inflammation by the stabilizing ligand, calmodulin.

Figure 3. 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.