RKIP and HMGA2 regulate breast tumor survival and metastasis through lysyl oxidase and syndecan-2

Abstract

Elucidating targets of physiological tumor metastasis suppressors can highlight key signaling pathways leading to invasion and metastasis. To identify downstream targets of the metastasis suppressor Raf Kinase Inhibitory Protein (RKIP/PEBP1), we utilized an integrated approach based upon statistical analysis of tumor gene expression data combined with experimental validation. Previous studies from our laboratory identified the architectural transcription factor and oncogene, HMGA2, as a target of inhibition by RKIP. Here we identify two signaling pathways that promote HMGA2-driven metastasis. Using both human breast tumor cells and an MMTV-Wnt mouse breast tumor model, we show that RKIP induces and HMGA2 inhibits expression of miR-200b; miR-200b directly inhibits expression of lysyl oxidase (LOX), leading to decreased invasion. RKIP also inhibits syndecan-2 (SDC2), which is aberrantly expressed in breast cancer, via down-regulation of HMGA2; but this mechanism is independent of miR-200. Depletion of SDC2 induces apoptosis and suppresses breast tumor growth and metastasis in mouse xenografts. RKIP, LOX, and SDC2 are coordinately regulated and collectively encompass a prognostic signature for metastasis-free survival in ER-negative breast cancer patients. Taken together, our findings reveal two novel signaling pathways targeted by the metastasis suppressor RKIP that regulate remodeling of the extracellular matrix and tumor survival.

Heparan sulfate signaling in cancer

“…These interactions frequently depend on the sulfation characteristics of the binding HSPG and mediate roles in adhesion that can affect cancer cell proliferation. For example, SDC2 promotes cell adhesion and associated proliferation, and decreasing SDC2 expression results in cell cycle arrest and decreased colon and breast cancer tumorigenesis [21, 22]. SDC2 is overexpressed in tumors of the breast, colon, prostate, and bladder, as well as gliomas and sarcomas [17].…”

Microenvironmental Influences on Metastasis Suppressor Expression and Function during a Metastatic Cell’s Journey

“…RKIP also de-represses GSK3β inhibition which, in turn, inhibits β-catenin, Snail and Slug activation with expected modulation of EMT [92]. Recent data, also from the Rosner group, show that RKIP induces and HMGA2 inhibits miR-200b expression which, in turn, inhibits expression of lysyl oxidase (LOX) [93]. Also via down-regulation of HMGA2, RKIP inhibits syndecan-2 independently of miR-200 [93].…”

“…Recent data, also from the Rosner group, show that RKIP induces and HMGA2 inhibits miR-200b expression which, in turn, inhibits expression of lysyl oxidase (LOX) [93]. Also via down-regulation of HMGA2, RKIP inhibits syndecan-2 independently of miR-200 [93].…”

Raf Kinase Inhibitory Protein (RKIP) as a Metastasis Suppressor: Regulation of Signaling Networks in Cancer

“…These analyses identified three additional downstream targets of RKIP and HMGA2: miR-200, lysine oxidase (LOX), and syn-decan 2 (SDC2). 42 miR-200 has been implicated in breast tumor cell initiation and the epithelial-mesenchymal transition that leads to cell invasion. 32 LOX is a known collagen and elastin cross-linker that helps invasion and metastasis.…”

“…This is confirmed by random survival forest (RSF) analysis of these genes, which showed that these genes cooperate in patient stratification, especially in low-RKIP tumors. Other gene signatures were also derived based on RKIP, HMGA2, LOX, and SDC2, 42 and the HMGA2, TET1, HOXAA7, and HOXA9 networks. 45 The general strategy for developing pathway gene signatures in this manner has been described previously.…”