The loss of DLG2 isoform 7/8, but not isoform 2, is critical in advanced staged neuroblastoma

Simon Keane,Katarina Ejeskär,Per Kogner,Tommy Martinsson

doi:10.1186/s12935-021-01851-w

Simon Keane, Katarina Ejeskär + Show 2 more

Open Access

https://doi.org/10.1186/s12935-021-01851-w

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Abstract

BackgroundNeuroblastoma is a childhood neural crest tumor showing large clinical and genetic heterogeneity, one form displaying 11q-deletion is very aggressive. It has been shown that 11q-deletion results in decreased expression of DLG2, a gene residing in the deleted region. DLG2 has a number of different isoforms with the main difference is the presence or absence of a L27 domain. The L27 domain containing DLG proteins can form complexes with CASK/MPP and LIN7 protein family members, which will control cell polarity and signaling.MethodsWe evaluated the DLG gene family and the LIN7 gene family for their expression in differently INSS staged neuroblastoma from publically available data and primary tumors, we included two distinct DLG1 and DLG2 N-terminal transcript isoforms encoding L27 domains for their expression. Functionality of DLG2 isoforms and of LIN7A were evaluated in the 11q-deleted neuroblastoma cell line SKNAS.ResultsIn neuroblastoma only two DLG2 isoforms were expressed: isoform 2 and isoform 7/8. Using the array data we could determine that higher expression of DLG members that contain L27 domains correlated to better survival and prognosis. Whilst DLG1 showed a decrease in both isoforms with increased INSS stage, only the full length L27 containing DLG2 transcripts DLG2-isoform 7/8 showed a decrease in expression in high stage neuroblastoma. We could show that the protein encoded by DLG2-isoform 7 could bind to LIN7A, and increased DLG2-isoform 7 gene expression increased the expression of LIN7A, this reduced neuroblastoma cell proliferation and viability, with increased BAX/BCL2 ratio indicating increased apoptosis.ConclusionWe have provided evidence that gene expression of the L27 domain containing DLG2-isoform 7/8 but not L27 domain lacking DLG2-isoform 2 is disrupted in neuroblastoma, in particular in the aggressive subsets of tumors. The presence of the complete L27 domain allows for the binding to LIN7A, which will control cell polarity and signaling, thus affecting cancer cell viability.

Highlights

Neuroblastoma is a childhood neural crest tumor showing large clinical and genetic heterogeneity, one form displaying 11q-deletion is very aggressive
In light of previous studies showing intriguing importance of Discs Large Homologue 2 (DLG2)-expression in NB [4, 5], we have in this study evaluated the expression of all Discs large homologue (DLG) and its different isoforms, especially considering the L27-domain containing DLG-isoforms, and the important L27 containing interaction partner Lin7 Homolog A (LIN7A) in NB
Unique DLG2 exons is used to encode the different DLG2 isoforms, the exon structure and initiation sites of the ζ, β, α, ε, δ and γ protein isoforms is presented in Fig. 1b [15, 16]

Summary

Introduction

Neuroblastoma is a childhood neural crest tumor showing large clinical and genetic heterogeneity, one form displaying 11q-deletion is very aggressive. It has been shown that 11q-deletion results in decreased expression of DLG2, a gene residing in the deleted region. Neuroblastoma (NB) is a transient embryonic neural crest pediatric tumor with development in the autonomous nervous system, in young children it is one of the most common form of extra cranial solid tumor [1]. The common genetic alterations that occur in aggressive (Stage 4) NB is the deletion of a segment of chromosome region 11q or amplification of the oncogene MYCN [2, 3]. Within the 11q-deleted region, resides the gene Discs Large Homologue 2 (DLG2). Low expression of DLG2 is seen in a majority of aggressive NBs, including both the 11q-deleted subset and those with MYCN amplification [4].

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