Sumoylated HSP-90 Is a Frequent Autosomal-Inherited Target of Paraproteins in Monoclonal Gammopathies

Background

Chronic antigenic stimulation might have a role in the pathogenesis of monoclonal gammopathy of unknown significance (MGUS) and multiple myeloma. We previously identified a group of 11 autoantigenic paraprotein targets (paratargs) of which paratarg-7 is the most frequent, found in ~15 % of all MGUS/MM/Waldenstrom patients. These paratarg autoantigens all have in common to be 1) recognised by patients paraprotein with an extreme high titer (>1:10¹¹), 2) hyperphosphorylated in patients, and 3) their phosphorylation carrier state is autosomal-dominant inherited in patients families. The finding that all these paratargs were permanently hyperphosphorylated in patients in contrast to healthy controls brought up the assumption that abnormal posttranslational modification of autoantigens might be a frequent finding in those patients.

Methods

A RZPD macroarray representing more than 30.000 different human proteins was subjected to in-vitro posttranslational modification using sumoylation-competent recombinant enzymes followed by screening with paraprotein-containing sera at high dilution (1:10⁷). Immunopositive signals were identified and characterized by DNA sequencing, SDS-PAGE, isoelectric focusing, western blotting and ELISA.

Findings

Twenty-seven of 226 (11.9%) paraproteins from European, 9/80 (11.2%) from African-American and 9/176 (5.1%) from Japanese patients reacted specifically with the sumoylated heat shock protein-90β isoform-α (HSP90-SUMO). No reactivity was detected in >800 controls. All patients with HSP90-SUMO-binding paraproteins carried HSP90-SUMO. HSP90-SUMO carrier state is autosomal-dominantly inherited and was sown to be caused by the inability of SENP2 to desumoylate HSP90-SUMO. Five of 550 (0.9%) European, 2/100 (2%) African-American and 2/178 (0.8%) Japanese controls carried HSP90-SUMO, resulting in odds ratios of 14.8, 6.2 and 7.4, respectively, of healthy carriers for MGUS/MM/WM. Only, but all MGUS/MM/WM patients who were HSP90-SUMO carriers had HSP90-SUMO-specific paraproteins suggesting that sumoylated HSP-90 is involved in the pathogenesis of MGUS/MM/WM by chronic antigenic stimulation. Demonstration of HSP90-SUMO carriership identifies family members of HSP90-SUMO patients at risk.

Interpretation

A significant proportion of MGUS/MM/WM are associated with a dominant inheritance of posttranslationally modified autoantigens as shown for members of the paratarg autoantigen family and for HSP90-SUMO, enabling family members at increased risk for MGUS/MMWM to be identified by simple analysis of their peripheral blood. That only patients with MGUS/MM/WM who are carriers of such modified autoantigens have target-specific paraproteins suggests that the posttranslational modification induces auto-immunity and is involved in the pathogenesis of MGUS/MM/WM, for example, by chronic antigenic stimulation.

Supported by Deutsche Forschungsgemeinschaft DFG, Deutsche José Carreras Leukämie Stiftung, Wilhelm-Sander-Stiftung, Deutsche Krebshilfe e.V.