Hokutan, Kanani

Purpose: Bladder cancer (BCa) is one of the most common cancer types worldwide and is characterized by a high rate of recurrence. In previous studies, we and others have described the functional influence of plasminogen activator inhibitor-1 (PAI1) in bladder cancer development. While polymorphisms in PAI1 have been associated with increased risk and worsened prognosis in some cancers, the mutational status of PAI1 in human bladder tumors has not been well defined. Methods: In this study, we evaluated the mutational status of PAI1 in a series of independent cohorts, comprised of a total of 660 subjects. Results: Sequencing analyses identified two clinically relevant 3′ untranslated region (UTR) single nucleotide polymorphisms (SNPs) in PAI1 (rs7242; rs1050813). Somatic SNP rs7242 was present in human BCa cohorts (overall incidence of 72%; 62% in Caucasians and 72% in Asians). In contrast, the overall incidence of germline SNP rs1050813 was 18% (39% in Caucasians and 6% in Asians). Furthermore, Caucasian patients with at least one of the described SNPs had worse recurrence-free survival and overall survival (p = 0.03 and p = 0.03, respectively). In vitro functional studies demonstrated that SNP rs7242 increased the anti-apoptotic effect of PAI1, and SNP rs1050813 was related to a loss of contact inhibition associated with cellular proliferation when compared to wild type. Conclusion: Further investigation of the prevalence and potential downstream influence of these SNPs in bladder cancer is warranted.

Abstract Sphingosine kinase 1 (SphK1) phosphorylates pro-apoptotic sphingosine to form pro-survival sphingosine-1-phosphate (S1P), leading to cancer progression. In breast cancer, high levels of SphK1 mRNA are found in 80% of the patients, with average increase of 2-fold in breast tumors compared with normal tissue from the same patient. Recent studies suggest that SphK1 expression is associated with disease-free survival in ER-negative and HER2-positive breast tumors. In addition, inhibition of SphK1 in HER2-positive breast cancer cell line reduced S1P-induced HER2 and ERK1/2 activation. While these evidences suggest that SphK1 may play an important role in HER2-positive breast cancer, the exact role of SphK1 in breast tumorigenesis remains unclear. The aim of this project is to define the role of SphK1 in HER2-positive breast tumorigenesis and to investigate whether the pathway components are potential target for breast cancer prevention and therapies. Here, we report that SphK1 is required for HER2/neu-induced breast tumorigenesis and SphK1 regulates claudin-2 (CLDN2) to promote tumor development perhaps by mediating HER2. In MMTV-neu transgenic mouse model, genetic deletion of SphK1, which was accompanied by reduced S1P and increased C16-ceramide levels, significantly inhibited breast tumor development, with reduced incidence (SphK1-/-, 19%; SphK1+/-, 26%; and SphK1+/+, 57%; p < 0.05) and multiplicity (SphK1-/-, 0.27 ± 0.13; SphK1+/-, 0.32 ± 0.07; and SphK1+/+, 0.67 ± 0.14 tumors per animal; p < 0.05). Unexpectedly, SphK1 deletion did not affect tumor growth as results showed no differences in tumor volume. However, this is not surprising when considering the fact that the tumors were allowed to grow until tumor reached 20 mm in longer diameter, at which they were sacrificed regardless of age. Interestingly, whole genome expression analysis by Illumina MouseWG-6 v2.0 Expression BeadChip Array revealed significant reduction of CLDN2 expression in tumors from SphK1 deficient mice (p < 0.0001). In support to these findings, overexpression of SphK1 in MDA-MB-453 human breast cancer cells, which HER2 is amplified but lacks hormone receptors, lead to increase in CLDN2 expression (p < 0.05). Furthermore, overexpression of SphK1 in MDA-MB-453 cells also enhanced cell proliferation, colony formation, and migration/invasion, and drug resistance to cisplatin. The relevance of this finings in humans was confirmed by immunostaining of SphK1 and CLDN2 in HER2-positive breast cancer tumors and normal tissues (n = 93 and 35 subjects, respectively). The results showed that the expression of SphK1 was higher in tumors compared to adjacent normal tissue (p < 0.0001). Furthermore, higher SphK1 expression was observed in high grade tumors (vs low grade; p < 0.001) and ER-PR- tumors (vs ER+PR+; p < 0.0001). Interestingly, we observed similar staining pattern of CLDN2 proteins, where CLDN2 expression was high in tumors (p < 0.0001), particularly in high grade tumors (p < 0.01) and ER-PR- tumors (p < 0.0001). Moreover, we found a strong correlation between SphK1 and CLDN2 expressions in tumors but not in normal tissues, confirming the results obtained in animal study. Taken together, these findings suggest that SphK1 may play a pivotal role in HER2-positive breast carcinogenesis, and targeting SphK1 and/or CLDN2 may represent a novel approach for HER2-positive breast cancer chemoprevention and/or treatment. Citation Format: Yoshiko Shimizu, Hideki Furuya, Paulette M. Tamashiro, Steve Goodison, Owen Chan, Ian Pagano, Kayoko Iino, Rafael Peres, Kanani Hokutan, Lenora W.M. Loo, Brenda Hernandez, Aung Naing, Charles J. Rosser, Toshihiko Kawamori. Genetic deletion of sphingosine kinase 1 suppresses mouse breast tumor development in MMTV-neu transgenic model. [abstract]. In: Proceedings of the AACR Special Conference on Advances in Breast Cancer Research; Oct 17-20, 2015; Bellevue, WA. Philadelphia (PA): AACR; Mol Cancer Res 2016;14(2_Suppl):Abstract nr B17.