Current diagnostic tools limit a clinician’s ability to discriminate between many possible causes of sensorineural hearing loss. This constraint leads to the frequent diagnosis of the idiopathic condition, leaving patients without a clear prognosis and only general treatment options. As a first step toward developing new diagnostic tools and improving patient care, we report the first use of liquid chromatography-tandem mass-spectrometry (LC-MS/MS) to map the proteome of human perilymph. Using LC-MS/MS, we analyzed four samples, two collected from patients with vestibular schwannoma (VS) and two from patients undergoing cochlear implantation (CI). For each cohort, one sample contained pooled specimens collected from five patients and the second contained a specimen obtained from a single patient. Of the 271 proteins identified with high confidence among the samples, 71 proteins were common in every sample, and used to conservatively define the proteome of human perilymph. Comparison to human cerebrospinal fluid and blood plasma, as well as murine perilymph, showed significant similarity in protein content across fluids; however, a quantitative comparison was not possible. Fifteen candidate biomarkers of VS were identified by comparing VS and CI samples. This list will be used in future investigations targeted at discriminating between VS tumors associated with good versus poor hearing.

Vestibular schwannomas (VSs) are the most common tumors of the cerebellopontine angle. Significant clinical need exists for pharmacotherapies against VSs. Motivated by previous findings that immunohistochemical expression of cyclooxygenase 2 (COX-2) correlates with VS growth rate, we investigated the role of COX-2 in VSs and tested COX-2 inhibiting salicylates against VSs. COX-2 was found to be aberrantly expressed in human VS and primary human VS cells in comparison to control human nerve specimens and primary Schwann cells (SCs), respectively. Further, levels of prostaglandin E2, the downstream enzymatic product of COX-2, correlated with primary VS culture proliferation rate. Because COX-2 inhibiting salicylates such as aspirin are well-tolerated and frequently clinically used, we assessed their repurposing for VS. Changes in proliferation, cell death and cell viability were analyzed in primary VS cultures treated with aspirin, sodium salicylate (NaSal) or 5-aminosalicylic acid (5-ASA). These drugs did not increase VS cell death nor affect healthy SCs. The cytostatic effect of aspirin in vitro was in concurrence with our previous clinical finding that VS patients taking aspirin demonstrate reduced tumor growth. Overall, this work suggests that COX-2 is a key modulator in VS cell proliferation and survival, and highlights salicylates as promising pharmacotherapies against VS.

The human T cell leukemia virus type 1 (HTLV-1) viral oncoprotein Tax acts as a transcriptional trans-activator affecting viral as well as cellular gene expression. To understand how Tax induces transformation, the consequences of its ability to alter expression of cellular genes must be examined. We have previously demonstrated that Tax activates expression of the cellular gene, proliferating cell nuclear antigen (PCNA), and that Tax suppresses DNA repair. In this study we tested the ability of previously described Tax mutants to activate PCNA gene expression and their ability to interfere with DNA repair. The results revealed a strong correlation between Tax trans-activation of PCNA gene expression and its ability to inhibit DNA repair via the nucleotide excision repair (NER) pathway. Thus, a consequence of activated PCNA gene expression appears to be reduced DNA repair capacity. These effects of Tax are likely to play important roles in its transforming activity.

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