Most patients with cancer-associated dermatomyositis have antibodies to nuclear matrix protein NXP-2 or transcription intermediary factor 1γ

Abstract

Objective: Since dermatomyositis (DM) is associated with an increased risk of malignancy, accurate identification of patients likely to harbor cancers is important. Using immunoprecipitations from radiolabeled cell lysates, several groups recently showed that anti-transcription intermediary factor 1γ (anti-TIF-1γ) antibodies are associated with malignancy in DM. We undertook this study to develop sensitive, specific assays to detect antibodies against TIF-1γ and nuclear matrix protein NXP-2 and to evaluate their association with malignancy in DM.

Methods: To detect anti-TIF-1γ antibodies, immunoprecipitations were performed using lysates made from HeLa cells overexpressing TIF-1γ, with detection by immunoblotting. Anti-NXP-2 antibodies were assayed by immunoprecipitation using (35) S-methionine-labeled NXP-2 generated by in vitro transcription/translation. We analyzed patient sera from DM cohorts seen at the Stanford University Dermatology Clinic (n = 111) and the Johns Hopkins Myositis Center (n = 102).

Results: A total of 17% and 38% of patients had antibodies against NXP-2 and TIF-1γ, respectively. Reactivity against either NXP-2 or TIF-1γ identified 83% of patients with cancer-associated DM. In addition to older age and male sex, cancer was associated with antibodies to NXP-2 or TIF-1γ on multivariate analysis (odds ratio 3.78 [95% confidence interval 1.33-10.8]). Stratification by sex revealed that anti-NXP-2 was specifically associated with cancer in males (odds ratio 5.78 [95% confidence interval 1.35-24.7]).

Conclusion: These studies demonstrate that anti-NXP-2 and anti-TIF-1γ antibodies are frequent DM specificities (found in 55% of patients) and are present in most patients with cancer-associated DM.

Figure 1

New assays to detect antibodies against transcription intermediary factor 1γ (TIF-1γ), nuclear matrix protein NXP-2, and melanoma differentiation–associated protein 5 (MDA-5). A, Immunoprecipitations (IP) were performed using ³⁵S-methionine (³⁵S-met)–labeled HeLa cell lysate with patient sera known to have antibodies against TIF-1γ, NXP-2, or MDA-5, as indicated (3 sera for each). A control serum and an alanyl–transfer RNA synthetase (PL-12)–positive reference serum were also included. B, Immunoprecipitations were performed with an anti–MDA-5 antibody–positive serum using ³⁵S-methionine–labeled HeLa cell lysate generated from cells incubated in the absence or presence of interferon (IFN) for 24 hours. C, Three sera from patients with dermatomyositis and 1 control serum were tested for antibodies by immunoprecipitation using ³⁵S-methionine–labeled MDA-5 or ³⁵S-methionine–labeled NXP-2 (in vitro transcription/translation immunoprecipitation [IVTT IP]), or by immunoprecipitation from TIF-1γ–transfected lysates followed by immunoblotting with anti–TIF-1γ monoclonal antibody (IP/Blot). These assays show that serum 9,078 is anti–MDA-5 positive, serum 9,020 is anti–NXP-2 positive, and serum 9,006 is anti–TIF-1γ positive.

Figure 2

Age and cancer distribution as a function of autoantibody status. A, Total numbers of patients in each age group for each antibody (Ab) class. Shaded portions of the bars represent actual numbers of patients with cancer-associated dermatomyositis (DM). B, Percentage of patients in each age group with cancer-associated DM. See Figure 1 for other definitions.