TY - JOUR
T1 - Unique conformation of cancer autoantigen B23 in hepatoma
T2 - A mechanism for specificity in the autoimmune response
AU - Ulanet, Danielle B.
AU - Torbenson, Michael
AU - Dang, Chi V.
AU - Casciola-Rosen, Livia
AU - Rosen, Antony
PY - 2003/10/14
Y1 - 2003/10/14
N2 - The association of a specific autoantibody response with distinct disease phenotypes is observed in both autoimmune diseases and cancer. Although the underlying mechanisms remain unclear, it is likely that unique properties of disease-specific autoantigens expressed in the relevant target cells play a role. It has recently been observed that the majority of autoantigens targeted across the spectrum of systemic autoimmune diseases (but not nonautoantigens) are selectively cleaved by the cytotoxic lymphocyte granule protease granzyme B (GB), generating unique fragments not observed during other forms of cell death. Although susceptibility of a molecule to cleavage by GB strongly predicts autoantigen status, the significance of this association is unclear. We used hepatocellular carcinoma and the hepatocellular carcinoma autoantigen, nucleophosmin/B23, as a model system to define the unique features of disease-specific autoantigens in the relevant disease microenvironment. These studies revealed a striking, selective susceptibility of B23 to cleavage by GB in extracts of neoplastic liver. The increased sensitivity of tumor B23 to proteolysis by GB was accompanied by slightly increased mobility on SDS/PAGE, altered subcellular localization, enrichment of an SDS-stable oligomeric form of B23, and recognition by a conformation-specific antibody detecting a B23 epitope ending at the GB cleavage site. In vitro studies demonstrated that this unique B23 conformation and resultant increased susceptibility to cleavage by GB arise when B23 translation is initiated at methionine-7. We propose that unique features of autoantigens in the disease-relevant microenvironment may regulate susceptibility to cleavage by GB and their selection by the specific autoimmune response.
AB - The association of a specific autoantibody response with distinct disease phenotypes is observed in both autoimmune diseases and cancer. Although the underlying mechanisms remain unclear, it is likely that unique properties of disease-specific autoantigens expressed in the relevant target cells play a role. It has recently been observed that the majority of autoantigens targeted across the spectrum of systemic autoimmune diseases (but not nonautoantigens) are selectively cleaved by the cytotoxic lymphocyte granule protease granzyme B (GB), generating unique fragments not observed during other forms of cell death. Although susceptibility of a molecule to cleavage by GB strongly predicts autoantigen status, the significance of this association is unclear. We used hepatocellular carcinoma and the hepatocellular carcinoma autoantigen, nucleophosmin/B23, as a model system to define the unique features of disease-specific autoantigens in the relevant disease microenvironment. These studies revealed a striking, selective susceptibility of B23 to cleavage by GB in extracts of neoplastic liver. The increased sensitivity of tumor B23 to proteolysis by GB was accompanied by slightly increased mobility on SDS/PAGE, altered subcellular localization, enrichment of an SDS-stable oligomeric form of B23, and recognition by a conformation-specific antibody detecting a B23 epitope ending at the GB cleavage site. In vitro studies demonstrated that this unique B23 conformation and resultant increased susceptibility to cleavage by GB arise when B23 translation is initiated at methionine-7. We propose that unique features of autoantigens in the disease-relevant microenvironment may regulate susceptibility to cleavage by GB and their selection by the specific autoimmune response.
KW - Granzyme B
KW - Hepatocellular carcinoma
KW - Nucleolus
KW - Oligomer
KW - Proteolysis
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U2 - 10.1073/pnas.2035245100
DO - 10.1073/pnas.2035245100
M3 - Article
C2 - 14519847
AN - SCOPUS:0142027755
SN - 0027-8424
VL - 100
SP - 12361
EP - 12366
JO - Proceedings of the National Academy of Sciences of the United States of America
JF - Proceedings of the National Academy of Sciences of the United States of America
IS - 21
ER -