Independent overexpression of the subunits of translation elongation factor complex eEF1H in human lung cancer

Abstract

BackgroundThe constituents of stable multiprotein complexes are known to dissociate from the complex to play independent regulatory roles. The components of translation elongation complex eEF1H (eEF1A, eEF1Bα, eEF1Bβ, eEF1Bγ) were found overexpressed in different cancers. To gain the knowledge about novel cancer-related translational mechanisms we intended to reveal whether eEF1H exists as a single unit or independent subunits in different human cancers.MethodsThe changes in the expression level of every subunit of eEF1H in the human non-small-cell lung cancer tissues were examined. The localization of eEF1H subunits was assessed by immunohistochemistry methods, subcellular fractionation and confocal microscopy. The possibility of the interaction between the subunits was estimated by co-immunoprecipitation.ResultsThe level of eEF1Bβ expression was increased more than two-fold in 36%, eEF1Bγ in 28%, eEF1A in 20% and eEF1Bα in 8% of tumor specimens. The cancer-induced alterations in the subunits level were found to be uncoordinated, therefore the increase in the level of at least one subunit of eEF1H was observed in 52% of samples. Nuclear localization of eEF1Bβ in the cancer rather than distal normal looking tissues was found. In cancer tissue, eEF1A and eEF1Bα were not found in nuclei while all four subunits of eEF1H demonstrated both cytoplasmic and nuclear appearance in the lung carcinoma cell line A549. Unexpectedly, in the A549 nuclear fraction eEF1A lost the ability to interact with the eEF1B complex.ConclusionsThe results suggest independent functioning of some fraction of the eEF1H subunits in human tumors. The absence of eEF1A and eEF1B interplay in nuclei of A549 cells is a first evidence for non-translational role of nuclear-localized subunits of eEF1B. We conclude the appearance of the individual eEF1B subunits in tumors is a more general phenomenon than appreciated before and thus is a novel signal of cancer-related changes in translation apparatus.

Non-translational Connections of eEF1B in the Cytoplasm and Nucleus of Cancer Cells

“…More than two-fold rise in the level of at least one eEF1B subunit was observed in 52% of 25 lung carcinoma samples. Again, the simultaneous increase in the level of all three eEF1B subunits was observed in one case, simultaneous upregulation of eEF1Bα and eEF1Bβ was also found in one case, simultaneous upregulation of eEF1Bβ and eEF1Bγ was observed in five cases while no correlated elevation of eEF1Bα and eEF1Bγ was found (Veremieva et al, 2014). The authors concluded that cancer-related upregulation of individual subunits rather than the whole eEF1B complex takes place in both cancers.…”

“…The levels of mRNA and a protein coded by this mRNA do not often correlate (Liu et al, 2016) which is valid for eEF1B subunits as well (Veremieva et al, 2011(Veremieva et al, , 2014Flores et al, 2016). This mini-review is focused on eEF1B proteins, therefore cancer-related changes in the levels of corresponding mRNAs are not considered here, although such changes may be of marker/prognostic importance (Hassan et al, 2018;Biterge-Sut, 2019).…”

“…An attempt to meet this challenge was undertaken in series of papers where cancer-related changes in the level of all three eEF1B subunits were analyzed simultaneously in the same tissue samples (Veremieva et al, 2011(Veremieva et al, , 2014. More than two-fold upregulation of at least one eEF1B subunit was observed in 72% of 25 cardioesophageal cancer samples.…”

“…As translation occurs in the cytoplasm then the cytoplasmic localization of eEF1B is obvious. However, signs of the nuclear localization of eEF1B subunits were displayed in the normal (Drosophila embryos, human cardioesophageal junction, human lung) and cancer (cardioesophageal carcinoma, lung cancer, oral squamous cell carcinoma) tissues as well as in lung adenocarcinoma cells A549 (Fan et al, 2010;Veremieva et al, 2011;Veremieva et al, 2014;Flores et al, 2016). In an attempt to attribute possible noncanonical eEF1B functions to the specific cellular compartments the partners of eEF1Bβ and eEF1Bγ in the cytoplasm and nucleus of human lung carcinoma cells were identified experimentally and analyzed by several bioinformatics approaches (Kapustian et al, 2016(Kapustian et al, , 2017(Kapustian et al, , 2018(Kapustian et al, , 2019.…”

Non-canonical interactions of the β subunit of the translation elongation complex eEF1B and analysis of their possible functional role

“…For a long time the eEF1B complex was considered very stable, however, recently we have found that some pool of its subunits could exist separately from the complex in different human cancer tissues [1][2][3]. The role of non-complexed subunits remains elusive.…”