Reduced RKIP Expression is Associated With Breast Neoplastic Progression and is Correlated With Poor Outcomes and Aberrant Methylation in Breast Carcinoma

Abstract

Raf kinase inhibitor protein's (RKIP) downregulation can predict poor outcome in patients with various types of malignancy. In this study, we aimed to assess the potential involvement of RKIP in breast carcinogenesis and to evaluate its association with outcome variables and aberrant promoter methylation in breast carcinoma (BC). Tissue microarray sections were immunostained for RKIP in 26 normal breasts, 25 usual ductal hyperplasia, 76 ductal carcinoma in situ, and 198 BC specimens. The methylation status of RKIP was also determined in BC. In addition, the mRNA and protein level of RKIP was analyzed in 8 pairs of BC tissues and surrounding normal tissues by quantitative real-time polymerase chain reaction and Western blot analysis, respectively. RKIP mRNA and protein expression was significantly downregulated in BC tissues compared with the surrounding normal tissues (P<0.05 and P<0.01, respectively). Reduced RKIP expression seemed to increase progressively from normal breast to BC (P<0.001). Reduced RKIP expression was significantly associated with metastatic relapse (P<0.001) and was identified as an independent adverse prognostic indicator for disease-free survival (P=0.003). Reduced RKIP expression in BC was significantly correlated with its aberrant promoter methylation (P<0.05). In conclusion, downregulation of RKIP plays an important role in the breast neoplastic progression and correlates with poor prognosis in patients with BC. Aberrant RKIP methylation is one of the mechanisms that lead to downregulation of RKIP in BC.

RKIP Regulates Differentiation-Related Features in Melanocytic Cells

“…Several studies have shown that RKIP exhibits low expression levels in various cancers and it is often absent in metastases [ 5 , 8 , 9 , 10 , 34 , 35 , 36 , 37 , 38 , 39 , 40 , 41 , 42 , 43 , 44 , 45 , 46 , 47 , 48 ]. In agreement, decreased RKIP expression has been associated with metastatic uveal melanoma while low levels of RKIP were detected on both metastatic as well as non-metastatic cutaneous melanoma biopsies [ 15 , 49 ].…”

“…RKIP is a multifunctional protein involved in carcinogenesis regulating cellular growth, motility, epithelial to mesenchymal transition and invasion [ 51 , 52 , 53 ]. Several authors have suggested that RKIP may not have a significant role in primary tumors but that instead, this protein could play an important role as a metastatic suppressor [ 5 , 8 , 9 , 10 , 34 , 35 , 36 , 37 , 38 , 39 , 40 , 41 , 42 , 43 , 44 , 45 , 46 , 47 , 48 ]. In this sense, and despite the described role for RKIP in the regulation of the MAPK/ERK pathway, RKIP has been implicated on the invasive behavior of malignant melanoma cells but not on their proliferative capability [ 14 ].…”

RKIP: A Key Regulator in Tumor Metastasis Initiation and Resistance to Apoptosis: Therapeutic Targeting and Impact

“…Several studies have shown that RKIP exhibits low expression levels in various cancers and it is often absent in metastasis [8,9,17,19,43,45,48,49,50,51,52,53,54,55,56,57,58,59,60]. RKIP loss has been suggested to result by hypermethylation of its promoter [41].…”

Targeting Raf Kinase Inhibitory Protein Regulation and Function

“…Promoter methylation: Promoter methylation is a well-characterized mechanism for epigenetic silencing by which gene transcription is halted through transcription factor inaccessibility, without any genetic alterations. Several studies of tumors, including gastric adenocarcinomas [ 18 , 19 ], esophageal squamous cell carcinomas [ 20 , 21 ], colorectal cancers [ 22 , 23 ], and breast cancers [ 24 ], reported that methylation status of the RKIP promoter determined by MSP (methylation specific PCR) strongly correlated with low RKIP expression levels in various advanced stages of the tumors. In gastric and esophageal cancers, carcinoma tissue showed significantly higher incidence rates of hypermethylated RKIP promoters than the adjacent normal mucosal tissue [ 19 , 21 ].…”

“…In agreement with these findings, patients whose tumors had hypermethylated RKIP showed worse overall survival rates compared to unmethylated RKIP cases in gastric cancers [ 19 ], implicating RKIP as an independent prognostic marker for survival. In a breast cancer study, however, methylation status of RKIP promoter did not predict survival independently [ 24 ], even though it strongly correlated with RKIP mRNA downregulation, which by itself was indicative of poor survival. This finding suggests other potential mechanisms for RKIP loss in advanced disease than just promoter methylation.…”