The histone code reader SPIN1 controls RET signaling in liposarcoma.

Henriette Franz,Dominica Willmann,Reinhard Buettner,Cordula Annette Jilg,Holger Greschik,Roland Schüle,Eva Wardelmann,Luka Ozretić,Manfred Jung

doi:10.18632/oncotarget.3000

Abstract

The histone code reader Spindlin1 (SPIN1) has been implicated in tumorigenesis and tumor growth, but the underlying molecular mechanisms remain poorly understood. Here, we show that reducing SPIN1 levels strongly impairs proliferation and increases apoptosis of liposarcoma cells in vitro and in xenograft mouse models. Combining signaling pathway, genome-wide chromatin binding, and transcriptome analyses, we found that SPIN1 directly enhances expression of GDNF, an activator of the RET signaling pathway, in cooperation with the transcription factor MAZ. Accordingly, knockdown of SPIN1 or MAZ results in reduced levels of GDNF and activated RET explaining diminished liposarcoma cell proliferation and survival. In line with these observations, levels of SPIN1, GDNF, activated RET, and MAZ are increased in human liposarcoma compared to normal adipose tissue or lipoma. Importantly, a mutation of SPIN1 within the reader domain interfering with chromatin binding reduces liposarcoma cell proliferation and survival. Together, our data describe a molecular mechanism for SPIN1 function in liposarcoma and suggest that targeting SPIN1 chromatin association with small molecule inhibitors may represent a novel therapeutic strategy.

Highlights

SPIN1 was initially described as an abundant maternal transcript deposited in the unfertilized mouse egg [1]
We show that SPIN1 is overexpressed in human liposarcoma compared to normal adipose tissue or lipoma
Screening tumor tissue arrays by immuno histochemistry with a SPIN1-specific antibody, we observed elevated SPIN1 protein levels in well-differentiated liposarcoma (WDLS), myxoid liposarcoma (MLS), dedifferentiated liposarcoma (DDLS), and pleomorphic liposarcoma (PLS) compared to normal adipose tissue or lipoma (Figure 1A, Supplementary 1A–1C)

Summary

Introduction

SPIN1 was initially described as an abundant maternal transcript deposited in the unfertilized mouse egg [1]. SPIN1 is a histone code reader composed of three tudor-like domains [11] shown to bind histone H3 trimethylated at lysine 4 (H3K4me3) [9, 10, 12, 13], a chromatin mark typically located at promoters and associated with active or poised genes [14]. H3K4me peptides interact with high affinity with an aromatic www.impactjournals.com/oncotarget pocket in the second tudor-like domain of SPIN1 [9, 13]. This association was recently shown to be further enhanced by the presence of asymmetrically dimethylated arginine 8 (H3R8me2a) [9], a mark implicated in the triggering of organizer gene expression [15]. Peptides harboring only the H3R8me2a modification bind to the first tudor-like domain of SPIN1 with low affinity [9], and mutation of either F141 or Y170 in the second tudor-like domain disrupts binding of H3K4me as well as H3K4me3-H3R8me2a peptides [9, 10]

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Conclusion