The histone code reader SPIN1 controls RET signaling in liposarcoma

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.

Developing Spindlin1 small-molecule inhibitors by using protein microarrays

“…SPIN1 null mice exhibit early post-natal lethality and display a defect in meiosis 41 . Finally, SPIN1 promotes RET signaling in liposarcoma 40 , where it was found that: 1) knockdown of SPIN1 in a liposarcoma cell line (T778) reduces cell proliferation, 2) proliferation rates are rescued with wild-type SPIN1, but not with a mutant in the Tudor domain that binds H3K4me3 (the interaction we are targeting), and 3) SPIN1 knockdown dramatically reduces tumor weight in a xenograft mouse model. This last finding could be adapted in the future, as an in vivo screening approach for the efficacy of the EML compounds.…”

“…Overexpression of SPIN1 induces transformation of NIH3T3 cells that acquire the ability to grow in soft agar and in nude mice 38 . SPIN1 protein levels are elevated in a number of different cancers 39,40 and the protein displays a diffuse nuclear localization and is enriched in nucleoli 29 . Mechanistically, SPIN1 functions as a “reader” of the histone H3K4me3 mark and coactivates transcription of rRNA genes, genes regulated by the MAZ transcription factor and Wnt target genes 29,40 .…”

“…SPIN1 protein levels are elevated in a number of different cancers 39,40 and the protein displays a diffuse nuclear localization and is enriched in nucleoli 29 . Mechanistically, SPIN1 functions as a “reader” of the histone H3K4me3 mark and coactivates transcription of rRNA genes, genes regulated by the MAZ transcription factor and Wnt target genes 29,40 . The interaction of SPIN1 with H3K4me3 is stabilized when a second Tudor domain engages the H3R8me2a mark 28 .…”

G protein pathway suppressor 2 (GPS2) acts as a tumor suppressor in liposarcoma

“…Besides the genetic amplification of the 12q13-15, other molecular mechanisms of LPS genesis have been proposed in recent years, including deregulation of some miRNAs and their downstream targets, epigenetics, and dysregulation of some oncogenic signaling pathways [4, 10, 28–31]. Particularly, amplification of the oncogene C-JUN is considered to contribute to the inhibition of PPARγ, a key regulator in terminal adipocyte differentiation [32].…”

Cellular analysis of the action of epigenetic drugs and probes

“…A positive example is a study on the role of the methyl lysine binding protein Spin1 (Spindlin1) in liposarcoma, where re-expression of Spin1 rescued the knockout phenotype but expression of a mutant that cannot bind H3K4me3 failed to do so. 5 This proves the dependency of the phenotype on an intact trimethyl lysine recognition and provided significant rationale for drug discovery approaches targeting Spindlin1. 6,7 For pharmacological experiments, reference compounds and negative controls are very important.…”