I received my Ph.D. from Baylor College of Medicine, Houston, TX in the Department of Cell Biology. After graduating from Baylor College of Medicine, I joined the laboratory of Dr. E.J. Benz, Jr., in the Division of Hematology, Department of Medicine at Johns Hopkins University, School of Medicine in 1998, to study protein 4.1R, a peripheral membrane protein that was originally discovered in red blood cells. In 2001, I moved to the laboratory of Dr. R.J. Bloch, in the Department of Physiology, at the University of Maryland School of Medicine, as an Academic Fellow, to study a small form of ankyrin 1 (small ankyrin 1) that localizes at the sarcoplasmic reticulum membranes, and its ligands in skeletal muscle. In 2002, I was promoted to Research Associate, and 2003 to Research Assistant Professor.
In 2007, I joined the Department of Biochemistry and Molecular Biology at the University of Maryland School of Medicine as Assistant Professor in the tenure track. Using the muscle and epithelial cell as model systems, my laboratory has pioneered the molecular and functional characterization of major cytoskeletal and membrane-associated proteins as structural and signaling mediators in health and disease. My research has been funded by grants from the Muscular Dystrophy Association (MDA), the American Heart Association (AHA) and the National Institutes of Health (NIH).
As evidence of the recognition of my group for its studies on cytoskeletal regulators, I have been invited to present our work in major national and international meetings, including the American Society for Cell Biology, the International Society for Heart Research, the Experimental Biology, the Biophysical Society, the Myofilament Meeting, the 20th World Congress on Advances in Oncology and 18th International Symposium of Molecular Medicine, the International Cancer Study & Therapy Conference etc.
In addition, I have been invited to serve in several study sections at NIH, AHA, MDA, and NSF, organize and chair symposia and satellite workshops, and serve as Lead Guest Editor in special issues for The Journal of Biotechnology and Biomedicine and Frontiers in Physiology. I am a member of the steering committee of the UMSOM Interdisciplinary Training Program in Muscle Biology funded by NIH/NIAMS, and the University of Maryland Marlene and Stewart Greenebaum Cancer Center-Program in Oncology.
My group has pioneered the molecular and functional characterization of the Obscurin and Myosin Binding Protein-C Slow subfamilies of cytoskeletal regulators in health and disease.
The obscurin subfamily:
Named due to initial difficulties in characterization and detection, obscurin is now understood to be a family of proteins (“obscurins”) expressed from the single OBSCN gene. The prototypical obscurin, obscurin A, is composed of 62 immunoglobulin (Ig) repeats interspersed with three fibronectin type-III (FNIII) domains and a calmodulin-binding IQ motif, followed by src homology-3 (SH3), tandem Rho-guanine nucleotide exchange factor (RhoGEF) and pleckstrin homology (PH) domains, two additional Ig repeats, and a non-modular COOH-terminal region of ~400 amino acids that contains consensus phosphorylation motifs for ERK kinases and ankyrin binding sites, yielding a total size of ~720 kDa (Fig. 1). Another giant isoform, obscurin B (~870 kDa), is similar to obscurin A, but lacks the COOH-terminal region. Instead, it includes two Ser/Thr kinase domains with homology to myosin light chain kinases, referred to as SK2 and SK1, which are preceded by Ig, and Ig and FNIII domains, respectively (Fig. 1). An alternative ribosomal entry site and start codon allow the expression of smaller obscurin isoforms, including a tandem kinase isoform that consists of partial SK2 and full length SK1, and a single kinase isoform that only contains SK1 (Fig. 1).
I. Molecular and Functional Characterization of Obscurins in Striated Muscles
Manipulation of the expression levels of obscurins, either in vitro or in vivo, has demonstrated that they play key roles in myofibrillogenesis, the cytoskeletal alignment of the sarcoplasmic reticulum membranes and the regulation of Ca2+ cycling, highlighting their importance in striated muscle structure and function (Fig. 2). This is further underscored by the dramatic up-regulation of obscurins in a myocardial hypertrophy mouse model and a ventricular tachycardia canine model. More importantly, recent genomic linkage analysis revealed the presence of >10 congenital mutations in the OBSCN gene that lead to the development of hypertrophic (HCM) and dilated (DCM) cardiomyopathy in humans.
II. Giant Obscurins in Breast Cancer Formation and Metastasis
Recent evidence has implicated the OBSCN gene in cancer development due to the high mutational prevalence it exhibits in different types of cancer, including breast cancer, leading to significant reduction of the obscurin transcript and protein levels. In light of this observation, we began to unravel the roles of the OBSCN gene in breast cancer formation and progression. Our studies were the first to show that giant obscurins are abundantly expressed in normal breast tissue, but are virtually absent from advanced stage human breast cancer biopsies (Fig. 3) and cell lines. Moreover, we demonstrated that normal breast epithelial cells depleted of giant obscurins exhibit dramatically increased survival, motility and invasiveness. Consistent with these findings, obscurin-knockdown (KD) breast epithelial cells fail to form adherens junctions and undergo Epithelial to Mesenchymal Transition (EMT). More importantly, obscurin-KD, but not scramble control, breast epithelial cells expressing an active form of K-Ras form extensive local (primary) tumors and lung metastases in vivo. We therefore postulate that giant obscurins act as growth and metastasis suppressors in normal breast epithelium.
The Myosin Binding Protein-C Slow (MyBP-C slow) subfamily:
We originally identified MyBP-C slow as a binding partner of giant obscurins in skeletal muscle. Given the molecular complexity, differential phosphorylation, key structural and regulatory roles, and direct involvement of MyBP-C slow in Distal Arthrogryposis Myopathies, the biology of the MyBP-C slow subfamily has become a major project in our laboratory.
III. MyBP-C Slow: a Multifaceted Regulator of Muscle Structure and Function
Myosin Binding Protein-C (MyBP-C) comprises a subfamily of thick filament associated proteins that has structural and regulatory roles. Three distinct isoforms have been characterized, including the cardiac, slow skeletal and fast skeletal. During the last forty years, numerous studies have focused on elucidating the mechanisms that modulate the activities of cardiac MyBP-C. On the contrary, the regulation and roles of the skeletal isoforms have remained obscure, and mainly inferred due to the structural similarity they share with cardiac MyBP-C. Our group has been studying the slow skeletal form of MyBP-C aiming to understand its regulation and activities. Using molecular tools, we have shown that the MYBPC1 gene, encoding MyBP-C slow, is heavily spliced giving rise to several variants, which are expressed in different combinations and amounts during development and in adulthood, in both slow and fast twitch skeletal muscles (Fig. 4). The slow variants share common domains, but differ by the inclusion or skipping of novel insertions located in the NH2-terminus, the FN-III C7 domain and the COOH-terminus. Both the NH2 and COOH termini can retain native myosin and actin and modulate the sliding velocity of actin filaments past myosin heads, though to different extents, and in a variant-specific manner. Moreover, using proteomic tools, we have demonstrated that MyBP-C slow undergoes extensive phosphorylation mediated by PKA and PKC. In particular, we have identified four phosphorylation sites in the NH2-terminus of the protein, with two of them located within alternatively spliced regions. Recently, mutations in MYBPC1 slow were directly associated with the development of different forms of arthrogryposis myopathy: Distal Arthrogryposis Type 1 and 2 (DA1 and DA2), which are severe autosomal dominant myopathies that selectively affect the distal limbs, and Lethal Congenital Contractural Syndrome Type 4 (LCCS4), a neonatal lethal autosomal recessive myopathy. We therefore postulate that MyBP-C slow plays important structural and regulatory roles in developing and adult skeletal muscles, via the expression of distinct variants that are differentially phosphorylated.
Current Lab Members:
Undergraduate Students (Summer 2016)
Assistant Professors (non-tenure track)