Phenylbutyrate inhibits growth of cervical carcinoma cells independent of HPV type and copy number

PURPOSE

Inhibitors of histone deacetylase, such as sodium butyrate, block proliferation of cervical carcinoma cells by inhibiting the G1 to S transition of the cell cycle. The derivative phenylbutyrate (PB), characterized by its higher pharmacological half-life, and its metabolite phenylacetate (PA) were tested for their growth-inhibitory function on cervical cancer cells differing in their HPV type, copy number, and integration sites.

METHODS AND RESULTS

Using flow cytometric and Western blot analyses, we show that a 24-h incubation period with PB, but not with PA, was already sufficient to cause a dose-dependent growth arrest by increasing the G1 fraction with a concomitant drop in the S-phase. Consistent with the cell cycle block, only PB, but not PA, induced the cyclin-dependent kinase inhibitors p21(CIP1) and p27(KIP1). The inhibitory effect was not the result of a non-specific cytotoxic effect of PB, since cessation of cellular growth was already completely reversible 5 h after drug removal.

CONCLUSIONS

Due to its broad growth inhibitory properties on different cervical carcinoma cells in vitro, and its low toxic profile demonstrated in preceding clinical studies, PB may serve as an effective drug in handling pre-cancerous lesions and cervical cancer in patients.

CD21 and FCRL5 form a receptor complex with robust B-cell activating capacity

The B-cell response to antigen is critically regulated by co-receptors. CD21 (complement receptor 2) amplifies the response to antigen linked to its ligands, specific C3 fragments. In contrast, human Fc receptor-like 5 (FCRL5), a novel IgG receptor, was reported to inhibit B-cell receptor (BCR) signaling. Here, we show that CD21 and FCRL5 physically associate, suggesting that immune complexes containing both C3 fragment and IgG could simultaneously engage the pre-assembled receptors. We found that activating signaling molecules such as CD19, active PLCγ2 and BTK were rapidly recruited to FCRL5 upon engagement, suggesting a novel activating function for FCRL5. We confirmed that FCRL5 through its ITIMs (immunoreceptor tyrosine-based inhibitory motif) inhibited BCR signaling in the absence of CD21 stimulation. In contrast, triple engagement of FCRL5, CD21 and the BCR led to a superior calcium response compared to CD21 and BCR co-stimulation, in both cell lines and tonsil B cells. Furthermore, the novel activating function was independent of established FCRL5 signaling motifs. While human peripheral B cells express either FCRL5 or CD21, we identified a sizable subset of tonsil B cells which co-express the two receptors. We propose that FCRL5 has dual signaling capacity, while CD21 co-engagement serves as molecular switch, converting FCRL5 from a negative to a positive co-receptor. In tissues, B cells that co-express FCRL5 and CD21 could robustly respond to IgG immune complexes loaded with C3 fragments.