Loss of Serum and Glucocorticoid-Regulated Kinase 3 (SGK3) Does Not Affect Proliferation and Survival of Multiple Myeloma Cell Lines
April
Loss of Serum and Glucocorticoid-Regulated Kinase 3 (SGK3) Does Not Affect Proliferation and Survival of Multiple Myeloma Cell Lines
Stefan Hausmann 0 1 2 3
Evelyn Brandt 0 1 2 3
Carolin Kchel 0 1 2 3
Hermann Einsele 0 1 2 3
Ralf C. Bargou 0 1 2 3
Ruth Seggewiss-Bernhardt 0 1 2 3
Thorsten Sthmer 0 1 2 3
0 Funding: This work was supported by the Wilhelm Sander-Stiftung (www.sanst.de)(Grant No. 2011.114.1 to RS-B, TS) and the Deutsche Forschungsgemeinschaft (www.dfg.de)(KFO 216 (RCB, HE , TS)). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript
1 Data Availability Statement: All relevant data are within the paper
2 Academic Editor: Richard Pearson, Peter MacCallum Cancer Centre , AUSTRALIA
3 1 Department of Internal Medicine II, Division of Hematology and Oncology, University Hospital of Wurzburg , Wurzburg, Germany , 2 Comprehensive Cancer Center Mainfranken, University Hospital of Wurzburg , Wurzburg , Germany
Multiple myeloma (MM) is a generally fatal plasma cell cancer that often shows activation of the phosphoinositide 3-kinase/Akt (PI3K/Akt) pathway. Targeted pharmacologic therapies, however, have not yet progressed beyond the clinical trial stage, and given the complexity of the PI3K/Akt signalling system (e.g. multiple protein isoforms, diverse feedback regulation mechanisms, strong variability between patients) it is mandatory to characterise its ramifications in order to better guide informed decisions about the best therapeutic approaches. Here we explore whether serum and glucocorticoid-regulated kinase 3 (SGK3), a potential downstream effector of PI3K, plays a role in oncogenic signalling in MM cells-either in concert with or independent of Akt. SGK3 was expressed in all MM cell lines and in all primary MM samples tested. Four MM cell lines representing a broad range of intrinsic Akt activation (very strong: MM.1s, moderate: L 363 and JJN-3, absent: AMO-1) were chosen to test the effects of transient SGK3 knockdown alone and in combination with pharmacological inhibition of Akt, PI3K-p110, or in the context of serum starvation. Although the electroporation protocol led to strong SGK3 depletion for at least 5 days its absence had no substantial effect on the activation status of potential downstream substrates, or on the survival, viability or proliferation of MM cells in all experimental contexts tested. We conclude that it is unlikely that SGK3 plays a significant role for oncogenic signalling in multiple myeloma.
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Competing Interests: The authors have declared
that no competing interests exist.
Multiple myeloma (MM) is a haematologic cancer caused by mature, antibody-producing
Bcells (plasma cells) [1]. It accounts for 10% of all haematological malignancies and has an
incidence rate in Europe of 4.5-6/100,000/year, affecting primarily the elderly population [2].
Due to ageing societies the incidence is thus continuously rising. Most patients have benefited
from the recent introduction of novel therapeutics such as proteasome inhibitors and IMiDs,
and survival parameters have shown substantial improvements over the last decade [3,4].
However, it has also become clear that the disease is characterised by a high degree of genetic
heterogeneity, potentially due to the long development time from monoclonal gammopathy of
undetermined significance (MGUS) to MM [5,6,7]. Truly targeted molecular therapies are thus
yet unavailable because actionable and/or broadly relevant therapeutic targets are missing.
One of the growth and survival pathways strongly implicated in MM pathogenesis is the
phosphoinositide 3-kinase/Akt (PI3K/Akt) pathway [8,9,10,11,12,13]. In addition to extrinsic
activation by microenvironmental factors [14] the pathway is often intrinsically active [10,15].
We have recently shown through isoform-specific knockdown analyses and with
isoform-specific pharmacologic inhibitors that the activity of PI3K, and specifically of the isoform p110,
is primarily required to maintain intrinsic Akt activation in MM cell lines [15]. The genetic
mechanisms underlying this oncogenic deregulation in MM are not entirely clear as some of
the lesions that could potentially be involved, such as PIK3CA mutation or PTEN deletion, are
too rare in this disease to be held fully accountable [16]. Pharmacologic blockade of
PI3Kp110 [15] or of Akt [10,11] is toxic to MM cell lines and primary MM cells, with intrinsic Akt
activation a good predictor for sensitivity to Akt blockade [10]. In addition, PI3K-p110 or
Akt blockade in concert with inhibition of the Ras/MAPK pathway often leads to enhanced
MM cell death [11,15]. However, for the Akt-independent MM cell line AMO-1 such a
combination effect is seen with PI3K/MEK1,2 inhibition but not with Akt/MEK1,2 inhibition
[11,15], arguing for the existence of PI3K-dependent contributions to MM cell survival that
can be independent of Akt.
A considerable number of pharmacologic inhibitor (...truncated)