Roswell Park Cancer Institute
Elm and Carlton Streets
Buffalo, New York USA 14263
Tel (lab):     716-845-5774 
Tel (office): 716-845-8540
Tel. (fax):    716-845-8906
E-mail: naveen.bangia@roswellpark.org

Welcome to the laboratory of Naveen Bangia, PhD in the Department of Immunology.  The research interests of the lab include:

• antigen presentation by MHC class I and MHC class II molecules
• the role of classical and non-classical MHC molecules in control of tumor growth
• the role of proteasome activator 200kD (PA200) in the cellular response to DNA damage.  

For inquiries about student, post doc or other research positions, please contact us by email.

  I. MHC Class I Antigen Presentation in Normal and Malignant Cells

Major histocompatibility complex (MHC or human HLA) class I molecules bind peptides largely derived from proteins made within the cell and display them at the cell surface for recognition by cytotoxic T lymphocytes (CTL). These ‘endogenously’ synthesized antigens may be of virus origin, or in the case of a tumor, they may be mutated or over expressed proteins that mark the tumor specifically. Recognition of the complex of an MHC class I molecule and peptide stimulates the CTL to eliminate the target cell. My laboratory is working to understand what is required for the formation and surface expression of this CTL target structure. Many proteins (see Figure) work together to generate this structure. These include:

• Proteasomes - are multicatalytic protease in the cytoplasm that generate peptides for transport
• TAP (Transporter associated with Antigen Processing) - a multi-membrane spanning heterodimer of two subunits (TAP1, TAP2) that transports peptides from the cytoplasm to the Endoplasmic Reticulum (ER) where the class I molecule waits
• Calreticulin and ERp57 - general ER chaperones that facilitate folding of proteins including MHC class I molecules
• Tapasin - a resident ER protein that links MHC class I molecules to TAP and promotes stable peptide binding by MHC class I molecules
• BAP31 – a multimembrane spanning molecule that can form homodimers or heterodimers with BAP29 to promote the export of many different protein out of the ER. Proteins that are known to be exported with the assistance of BAP31 include immunoglobulin D (IgD), MHC class I molecules, cellubrevin and cystic fibrosis transmembrane conductance regulator (CFTR).

MHC Class I Antigen Presentation

One goal is to understand how tapasin functions to enhance TAP levels and how tapasin, ERp57 and calreticulin work together to assemble class I molecules with their peptide ligand in the ER and allow transport to the cell surface.

A second goal is to understand how tumors may downregulate MHC class I molecules from the cell surface to potentially evade CTL recognition. We have identified a novel melanoma cell line that lacks MHC class I expression at the cell surface due to defective tapasin protein expression (Belicha-Villanueva et. al. manuscript submitted).

II. The Role of Proteasome Activator 200, PA200, in Response to DNA Damage

Proteasome Activator 200kD (PA200)

Proteasome activator 200kD is a nuclear localized protein that is conserved from S. cerevisiae to humans. In vitro, PA200 enhances the activity of proteasomes. Upon DNA damage by exposure to ionizing radiation (IR), PA200 relocalizes from its diffuse nuclear distribution to punctate nuclear structures (foci or dots) similar to that observed for proteins involved in DNA repair. Based on these observations, it has been speculated that PA200 is involved in DNA repair, however direct evidence for this idea has not been reported to date. Our laboratory has obtained further evidence that PA200 and proteasomes respond to DNA damage by relocalizing to chromatin resulting in increased proteolytic activity. Ongoing investigations in the laboratory are aimed at identifying the key proteins that are degraded with the assistance of PA200. Since PA200 enhances proteasome mediated proteolysis in vitro and all detectable PA200 within cells is associated with core proteasomes, the function of PA200 in the cellular response is likely linked to its association with proteasomes; one of the major proteolytic enzymes within the cell.

Cellular Proteasomes

Proteasomes are comprised of a barrel shaped core particle that is associated with different regulators (or caps) which bind to its ends. The core proteasome is comprised of four heptameric ring structures stacked upon each other. The outer rings consist of α subunits, while the two middle rings consist of β subunits. Three catalytic β subunits confer the three proteolytic specificities of proteasomes; tryptic, chymotryptic and post-glutamyl activities. These three catalytic β subunits are replaced by three β subunits that are inducible by the cytokine interferon gamma (IFNγ). Proteasomes are located throughout the cytosol and the nucleus, however, their catalytic sites are protected within the barrel core and their activity is regulated by caps at either end. Both of these properties ensure that proteolytic cleavage is regulated and specific.

Two different caps that associate with the ends of core proteasomes have been well characterized. 19S caps (also called PA700 cap) consist of multiple subunits that are responsible for recognition of ubiquitin, ubiquitin cleavage, protein unfolding and insertion into the core proteasome. 19S caps associated with core proteasomes are termed 26S proteasomes which are capable of degrading proteins that have been covalently modified by the addition of multiple ubiquitin moieties. Early studies suggested that a single proteasome, capped by a 19S cap on either end gave rise to 26S proteasomes. However, more recent studies have identified proteasomes with a 19S cap on one end and a PA28 (or 11S) cap on the other end.

PA28 or 11S caps are comprised of PA28α and PA28β which are inducible upon exposure of cells to IFNγ. Since IFNγ is known to enhance immune responses and antigen presentation, core proteasomes (with the three β subunit substitutions) associated with 11S caps (or so-called immunoproteasomes) are thought to promote the generation of peptides that are more appropriate for binding to Major Histocompatibility Complex (MHC) class I molecules.

PA200 may represent a third cap and regulator of proteasomes because in vitro, mammalian PA200 enhances proteasome mediated peptide hydrolysis. Furthermore, the yeast homolog of PA200, Blm10 (previously termed Blm3), associates with the ends of core proteasomes. Our preliminary data demonstrate that hybrid proteasomes consisting of a core proteasome with a PA200 protein on one end and a 19S cap on the other is enhanced after exposure to IR. The fact that PA200 and 19S caps likely associate with the same core proteasome suggests that PA200 may modulate the degradation of ubiquitinated proteins within cells. The current projects in the laboratory are aimed at understanding a) how important PA200 is for the survival of cells from DNA damage, b) the signals that recruit PA200 to the chromatin and c) the specific substrate proteins that are degraded with the assistance of PA200.