Stage II colon cancer patients with low levels of nuclear pRKIP experienced longer recurrence free survival compared to that of patients with high levels. The interaction between RKIP and Raf 1 has been shown to play an important role in CRC survival by suppressing metastasis worldwide distributors through the down regulation of Raf 1 and the up regulation of RKIP. Fur thermore, when RKIP expression in CRC is down regulated in the cytoplasm, increased vascular invasion and poor patient prognosis are observed. Significantly, RKIP, peritoneal invasion and LVI provide independent prognostic information in Dukes B CRC patients. As previously shown, increased expression of RKIP in breast and prostate cancer cells leads to increased sensitization to chemotherapeutic agent as measured by CPT induced apoptosis, a similar mechanism may explain the role of RKIP in the resistance to chemotherapeutic agents in CRC patients.

Another mechanism of therapeutic resistance relating RKIP to the KEAP1 NRF2 pathway has been described. Apoptosis was associated with the RKIP KEAP1 expression levels in colorectal cancer tissues, providing another mechanism by which diminution of RKIP levels may result in resistance to therapy. Previous studies show that protein kinase C is responsible for the direct phosphorylation of RKIP, our study has demonstrated that cell survival signaling caused by IL 6 leads to phosphorylation of RKIP. Since high IL 6 levels are linked to tumor growth and progression in colon cancer it is logical that we also observed increased levels of pRKIP in these patients.

The association between IL 6, pRKIP, and patient survival illustrates the necessity for delineating the mechanism to inhibit the phosphorylation. Previously, IL 6 has been shown to activate STAT3 in colon cancer through phosphorylation on the tyrosine 705 residue. Our results suggest that IL 6 triggered STAT3 phos phorylation and activation is correlated with the increase in pRKIP and thus the stimulation of the Raf MEK ERK survival pathway. Whether IL 6 stimulation leads to the activation of PKC or other kinase pathways leading to RKIP AZD-2281 phosphoryl ation directly or if this event is associated with the phosphoryl ation of STAT3 is currently under investigation. Based on our IHC observations, we further investigated the phosphorylation levels of STAT3. IHC analysis revealed that lower levels of nuclear STAT3 are associated with less invasive tumors and the nuclear expression of STAT3 is significantly associated with high grade tumors and the presence of lymphovascular invasion. Recent studies have demonstrated details about the STAT3 nuclear localization mechanism and have blocked this localization in human multiple myeloma cells.