BackgroundMUC16 is a cell surface mucin expressed at high levels by epithelial ovarian tumors. Following proteolytic cleavage, cell surface MUC16 (csMUC16) is shed in the extracellular milieu and is detected in the serum of cancer patients as the tumor marker CA125. csMUC16 acts as an adhesion molecule and facilitates peritoneal metastasis of ovarian tumors. Both sMUC16 and csMUC16 also protect cancer cells from cytotoxic responses of natural killer (NK) cells. In a previous study we demonstrated that sMUC16 binds to specific subset of NK cells. Here, we identify the csMUC16/sMUC16 binding partner expressed on immune cells.ResultsAnalysis of immune cells from the peripheral blood and peritoneal fluid of ovarian cancer patients indicates that in addition to NK cells, sMUC16 also binds to B cells and monocytes isolated from the peripheral blood and peritoneal fluid. I-type lectin, Siglec-9, is identified as the sMUC16 receptor on these immune cells. Siglec-9 is expressed on approximately 30-40% of CD16pos/CD56dim NK cells, 20-30% of B cells and >95% of monocytes. sMUC16 binds to the majority of the Siglec-9pos NK cells, B cells and monocytes. sMUC16 is released from the immune cells following neuraminidase treatment. Siglec-9 transfected Jurkat cells and monocytes isolated from healthy donors bind to ovarian tumor cells via Siglec-9-csMUC16 interaction.ConclusionsRecent studies indicate that csMUC16 can act as an anti-adhesive agent that blocks tumor-immune cell interactions. Our results demonstrate that similar to other mucins, csMUC16 can also facilitate cell adhesion by interacting with a suitable binding partner such as mesothelin or Siglec-9. Siglec-9 is an inhibitory receptor that attenuates T cell and NK cell function. sMUC16/csMUC16-Siglec-9 binding likely mediates inhibition of anti-tumor immune responses.

BackgroundCancer cells utilize a variety of mechanisms to evade immune detection and attack. Effective immune detection largely relies on the formation of an immune synapse which requires close contact between immune cells and their targets. Here, we show that MUC16, a heavily glycosylated 3-5 million Da mucin expressed on the surface of ovarian tumor cells, inhibits the formation of immune synapses between NK cells and ovarian tumor targets. Our results indicate that MUC16-mediated inhibition of immune synapse formation is an effective mechanism employed by ovarian tumors to evade immune recognition.ResultsExpression of low levels of MUC16 strongly correlated with an increased number of conjugates and activating immune synapses between ovarian tumor cells and primary naïve NK cells. MUC16-knockdown ovarian tumor cells were more susceptible to lysis by primary NK cells than MUC16 expressing controls. This increased lysis was not due to differences in the expression levels of the ligands for the activating receptors DNAM-1 and NKG2D. The NK cell leukemia cell line (NKL), which does not express KIRs but are positive for DNAM-1 and NKG2D, also conjugated and lysed MUC16-knockdown cells more efficiently than MUC16 expressing controls. Tumor cells that survived the NKL challenge expressed higher levels of MUC16 indicating selective lysis of MUC16low targets. The higher csMUC16 levels on the NKL resistant tumor cells correlated with more protection from lysis as compared to target cells that were never exposed to the effectors.ConclusionMUC16, a carrier of the tumor marker CA125, has previously been shown to facilitate ovarian tumor metastasis and inhibits NK cell mediated lysis of tumor targets. Our data now demonstrates that MUC16 expressing ovarian cancer cells are protected from recognition by NK cells. The immune protection provided by MUC16 may lead to selective survival of ovarian cancer cells that are more efficient in metastasizing within the peritoneal cavity and also at overcoming anti-tumor innate immune responses.

We identified cell surface markers associated with repression of p16 INK4a

Objectives The incidence of chemotherapy induced peripheral neuropathy (CIPN) is 15–25% with platinum and taxanes. CIPN can be permanent and often requires dose reduction or change in chemotherapy. Acetyl-L-carnitine (ALCAR), an ester of L-carnitine, is used to treat CIPN in humans and in animal models. The goals of this study are: 1) examine the effects of ALCAR on ovarian cancer cells, 2) determine if ALCAR affects the cytotoxicity of standard chemotherapy on ovarian cancer cells. Methods OVCAR-3 and SKOV-3 ovarian cancer lines were incubated in ALCAR containing media. Viability, proliferation, and expression of the nerve growth factor receptors (NGFR) Trk-A and p-75 were determined by flow cytometry. Cytotoxicity assays examining ALCAR’s effect on paclitaxel and carboplatin were done by flow cytometry and infrared plate-reader. Results Flow cytometry showed no change in percent live (p=0.87) or proliferation (p=0.95) of OVCAR-3 cells when comparing controls with up to 100 μM ALCAR. However, there was a slight but significant decrease in the proliferation of SKOV-3 cells incubated at higher ALCAR concentrations (p=<0.01). Flow cytometry showed no difference in the viability of OVCAR-3 cells when comparing ALCAR: +/− paclitaxel (p=1), +/− carboplatin (p=0.8), or both (p=0.4). Proliferation assays indicated that paclitaxel’s cytotoxicity on OVCAR-3 and SKOV-3 cells was unchanged at higher ALCAR concentrations (p=<0.01–0.4). ALCAR did not affect the expression of NGFR on OVCAR-3 or SKOV-3 cells. Conclusion ALCAR does not affect the cytotoxicity of paclitaxel or carboplatin. There was no increase in proliferation, or NGFR of OVCAR-3 or SKOV-3 cells exposed to ALCAR.