A Monoclonal Antibody to M-Phase Phosphoprotein 1/Kinesin-Like Protein KIF20B

Anti-KIF20B autoantibodies are associated with cranial neuropathy in systemic lupus erythematosus

BACKGROUND

Cranial neuropathies (CN) are a rare neuropsychiatric SLE (NPSLE) manifestation. Previous studies reported that antibodies to the kinesin family member 20B (KIF20B) (anti-KIF20B) protein were associated with idiopathic ataxia and CN. We assessed anti-KIF20B as a potential biomarker for NPSLE in an international SLE inception cohort.

METHODS

Individuals fulfilling the revised 1997 American College of Rheumatology (ACR) SLE classification criteria were enrolled from 31 centres from 1999 to 2011 and followed annually in the Systemic Lupus Erythematosus International Collaborating Clinics inception cohort. Anti-KIF20B testing was performed on baseline (within 15 months of diagnosis or first annual visit) samples using an addressable laser bead immunoassay. Logistic regression (penalised maximum likelihood and adjusting for confounding variables) examined the association between anti-KIF20B and NPSLE manifestations (1999 ACR case definitions), including CN, occurring over the first 5 years of follow-up.

RESULTS

Of the 1827 enrolled cohort members, baseline serum and 5 years of follow-up data were available on 795 patients who were included in this study: 29.8% were anti-KIF20B-positive, 88.7% female, and 52.1% White. The frequency of anti-KIF20B positivity differed only for those with CN (n=10) versus without CN (n=785) (70.0% vs 29.3%; OR 5.2, 95% CI 1.4, 18.5). Compared with patients without CN, patients with CN were more likely to fulfil the ACR haematological (90.0% vs 66.1%; difference 23.9%, 95% CI 5.0%, 42.8%) and ANA (100% vs 95.7%; difference 4.3%, 95% CI 2.9%, 5.8%) criteria. In the multivariate analysis adjusting for age at baseline, female, White race and ethnicity, and ACR haematological and ANA criteria, anti-KIF20B positivity remained associated with CN (OR 5.2, 95% CI 1.4, 19.1).

CONCLUSION

Anti-KIF20B is a potential biomarker for SLE-related CN. Further studies are needed to examine how autoantibodies against KIF20B, which is variably expressed in a variety of neurological cells, contribute to disease pathogenesis.

Anti-KIF20B autoantibodies in systemic autoimmune rheumatic diseases: Their high prevalence in systemic lupus erythematosus

The kinesin superfamily protein 20B (KIF20B), also known as M-phase phosphoprotein-1, is a plus-end-directed motor enzyme for cytokinesis. Anti-KIF20B antibodies have been reported in idiopathic ataxia, but no previous studies have examined anti-KIF20B antibodies in systemic autoimmune rheumatic diseases (SARDs). We aimed to establish methods for detecting anti-KIF20B antibodies and to investigate the clinical significance of these antibodies in SARDs. Serum samples from 597 patients with various SARDs and 46 healthy controls (HCs) were included. Fifty-nine samples that had been examined by immunoprecipitation using the recombinant KIF20B protein produced by in vitro transcription/translation were used for establishing the ELISA cutoff with the same recombinant protein for measuring the anti-KIF20B antibodies. The ELISA performed well, showing close agreement with the immunoprecipitation results (Cohen's κ >0.8). The ELISA results for 643 samples showed the prevalence of anti-KIF20B to be higher in the systemic lupus erythematosus (SLE) patients than in the HCs (18/89 vs. 3/46, P = 0.045). Since no SARD other than SLE had higher frequencies of anti-KIF20B antibodies than those of the HCs, we investigated the clinical characteristics of anti-KIF20B antibody-positive cases in SLE. The score on the SLE Disease Activity Index-2000 (SLEDAI-2K) was significantly higher for the anti-KIF20B-positive SLE patients than for the anti-KIF20B-negative SLE patients (P = 0.013). In a multivariate regression analysis of the anti-single-stranded deoxyribonucleic acid, anti-double-stranded deoxyribonucleic acid, and anti-KIF20B antibodies, the presence of anti-KIF20B antibody was significantly associated with high SLEDAI-2K scores (P = 0.003). Anti-KIF20B antibodies were found in ~20% of patients with SLE and were associated with high SLEDAI-2K scores. Much larger cohort and longitudinal studies are needed to confirm the association between anti-KIF20B antibodies and SLE.

Single-motor and multi-motor motility properties of kinesin-6 family members

Kinesin motor proteins are responsible for orchestrating a variety of microtubule-based processes including intracellular transport, cell division, cytoskeletal organization, and cilium function. Members of the kinesin-6 family play critical roles in anaphase and cytokinesis during cell division as well as in cargo transport and microtubule organization during interphase, however little is known about their motility properties. We find that truncated versions of MKLP1 (HsKIF23), MKLP2 (HsKIF20A), and HsKIF20B largely interact statically with microtubules as single molecules but can also undergo slow, processive motility, most prominently for MKLP2. In multi-motor assays, all kinesin-6 proteins were able to drive microtubule gliding and MKLP1 and KIF20B were also able to drive robust transport of both peroxisomes, a low-load cargo, and Golgi, a high-load cargo, in cells. In contrast, MKLP2 showed minimal transport of peroxisomes and was unable to drive Golgi dispersion. These results indicate that the three mammalian kinesin-6 motor proteins can undergo processive motility but differ in their ability to generate forces needed to drive cargo transport and microtubule organization in cells.

Role of autoantibodies and blood-brain barrier leakage in cognitive impairment in systemic lupus erythematosus

Objective

Cognitive impairment is common in patients with SLE but the cause is unknown. The current cross-sectional study examined the association between select SLE-related autoantibodies, other serological biomarkers and extensive blood–brain barrier (BBB) leakage in patients with SLE with and without cognitive impairment. In addition, we determined whether the relationship between SLE autoantibodies, other biomarkers and cognitive impairment differed depending on the presence or absence of concurrent extensive BBB leakage.

Methods

Consecutive patients with SLE, recruited from a single academic medical centre, underwent formal neuropsychological testing for assessment of cognitive function. On the same day, BBB permeability was determined using dynamic contrast-enhanced MRI scanning. SLE autoantibodies and other serological biomarkers were measured. Regression modelling was used to determine the association between cognitive impairment, extensive BBB leakage and autoantibodies/biomarkers.

Results

There were 102 patients with SLE; 90% were female and 88% were Caucasian, with a mean±SD age of 48.9±13.8 years. The mean±SD SLE disease duration was 14.8±11.0 years. Impairment in one or more cognitive tests was present in 47 of 101 (47%) patients and included deficits in information processing speed (9%), attention span (21%), new learning (8%), delayed recall (15%) and executive abilities (21%). Extensive BBB leakage was present in 20 of 79 (25%) patients and was associated with cognitive impairment (15 of 20 (75%) vs 24 of 59 (41%); p=0.01) and shorter disease duration (median (IQR): 7 (8–24 years) vs 15 (2–16 years); p=0.02). No serological parameters were associated with extensive BBB leakage and there was no statistically significant association between cognitive impairment and circulating autoantibodies even after adjusting for BBB leakage.

Conclusions

Extensive BBB leakage alone was associated with cognitive impairment. These findings suggest that BBB leakage is an important contributor to cognitive impairment, regardless of circulating SLE-related autoantibodies.