Modulation of TGFbeta 2 levels by lamin A in U2-OS osteoblast-like cells: understanding the osteolytic process triggered by altered lamins.

Camilla Evangelisti,Giuseppe Novelli,Maria Rosaria D’Apice,Nicola Baldini,Stefano Squarzoni,Giovanna Lattanzi,Sabino Prencipe,Silvia Lemma,Pia Bernasconi,Alberto M Martelli,Paola Cavalcante,Cristina Cappelletti,Sofia Avnet,Paolo Sbraccia

doi:10.18632/oncotarget.3232

Abstract

Transforming growth factor beta (TGFbeta) plays an essential role in bone homeostasis and deregulation of TGFbeta occurs in bone pathologies. Patients affected by Mandibuloacral Dysplasia (MADA), a progeroid disease linked to LMNA mutations, suffer from an osteolytic process. Our previous work showed that MADA osteoblasts secrete excess amount of TGFbeta 2, which in turn elicits differentiation of human blood precursors into osteoclasts. Here, we sought to determine how altered lamin A affects TGFbeta signaling. Our results show that wild-type lamin A negatively modulates TGFbeta 2 levels in osteoblast-like U2-OS cells, while the R527H mutated prelamin A as well as farnesylated prelamin A do not, ultimately leading to increased secretion of TGFbeta 2. TGFbeta 2 in turn, triggers the Akt/mTOR pathway and upregulates osteoprotegerin and cathepsin K. TGFbeta 2 neutralization rescues Akt/mTOR activation and the downstream transcriptional effects, an effect also obtained by statins or RAD001 treatment. Our results unravel an unexpected role of lamin A in TGFbeta 2 regulation and indicate rapamycin analogs and neutralizing antibodies to TGFbeta 2 as new potential therapeutic tools for MADA.

Highlights

The nuclear envelope is a master regulator of several cellular functions thanks to its ability to modulate transcription and chromatin arrangement in response to external stimuli [1]
Our results show that lamin A is able to modulate TGFbeta 2 levels, while its mutated form found in Mandibuloacral Dysplasia (MADA) causes excess levels of this cytokine and triggers elevated OPG and cathepsin K amount through activation of the Akt/mammalian target of rapamycin (mTOR) pathway
To get insights into the effect of lamins on TGFbeta 2 regulation, U2-OS cells were transfected with FLAG-tagged plasmids expressing wild-type prelamin A (WT), which is produced as mature lamin A, or uncleavable prelamin A (L647R), which yields accumulation of farnesylated prelamin A

Summary

Introduction

The nuclear envelope is a master regulator of several cellular functions thanks to its ability to modulate transcription and chromatin arrangement in response to external stimuli [1]. An interplay with the nuclear envelope has been demonstrated for diverse signaling effectors such as extracellular signal-regulated kinases (ERK) 1/2, c-Fos [2], Wnt/b-catenin [3], Akt/mammalian target of rapamycin (mTOR) [4, 5], TGFbeta 1 and 2 [6,7,8]. TGF beta signaling may regulate bone remodeling, acting on osteoblast and osteoclast homeostasis [15]. TGF beta is produced by osteoblasts [16], synthesized in a biologically inactive form [17] and deposited into the bone matrix [18], www.impactjournals.com/oncotarget where it is released and activated during bone resorption [19]. TGFbeta 2 is considered a primer of hematopoietic precursor fate, acting on monocytes to commit them to osteoclastogenesis [15]

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Conclusion