LATS Young Investigator Awards

Lais S. Moraes

Winner 2017

ABI3, a link between PI3K/AKT and WAVE regulatory complex?

Lais S. Moraes, Nilson I T Zanchin e Janete M Cerutti

Genetic Bases of Thyroid Tumors Laboratory, Division of Genetics, Department of Morphology and
Genetics, Escola Paulista de Medicina, Universidade Federal de São Paulo, SP, Brazil
Instituto Carlos Chagas, Fundação Oswaldo Cruz/FIOCRUZ, Curitiba, Paraná, Brazil

Introduction: We have previously reported that ABI3 expression is lost in most
follicular thyroid carcinomas. Restoration of ABI3 expression in a follicular thyroid
cancer cell line (WRO), significantly inhibited cell growth, invasiveness, migration and
reduced tumor growth in vivo. We further demonstrated that ABI3 is epigenetically
silenced by promoter methylation in follicular thyroid carcinomas, suggesting that ABI3
is a tumor suppressor gene. However, little is known about the molecular mechanism
by which ABI3 exercises these tumor suppressive effects in thyroid cells.
Objectives: To investigate the molecular mechanism by which ABI3 exerts its tumor
suppressive effects in FTC.
Methods: Cell lysates from WRO cells stably transfected with either ABI3 or control
were incubated with Human Phospho-Kinase Array Kit and Human Apoptosis Array Kit.
In order to visualize enriched pathways, Kinase Enrichr analysis (KEA) tool was used.
The immunoprecipitation combined with mass spectrometry (LC-MS/MS) was used to
identify ABI3-interacting proteins.
Results: We here show, for the first time, that ABI3 is a phosphoprotein that modulated
distinct cancer-related pathways in thyroid cancer cells. When we applied KEA
analysis, an alternative approach to recognize signaling pathways, we found that PI3K
substrates were enriched. The expression of PI3K/AKT pathway components were
confirmed in two follicular thyroid carcinoma cells (WRO and FTC133) by western blot.
Forced expression of ABI3 in WRO and FTC133 markedly decreased the
phosphorylation of AKT (T308 and S473) and the downstream-targeted protein
pGSK3β (S9). With immunoprecipitation we identify ABI3-interacting proteins that may
be involved in modulating or even integrating signaling pathways. We identified 37
ABI3 partners, including several components of the canonical WAVE regulatory
complex (WRC). These findings suggested that ABI3 function might be regulated
through this protein complex. Both, pharmacological inhibition of the PI3K/AKT
pathway and mutation at residue S342 of ABI3, which is predicted to be
phosphorylated by AKT, provided evidences that the non-phosphorylated form of ABI3
is preferentially present in the WRC protein complex.

Conclusion: Our findings suggest non-phosphorylated form of ABI3 might be
associated with its tumor suppressor effects and that ABI3 might link PI3K/AKT with
WRC complex.