Down-Regulation of Class II Phosphoinositide 3-Kinase α Expression below a Critical Threshold Induces Apoptotic Cell Death

Abstract

Members of the phosphoinositide 3-kinase (PI3K) family collectively control multiple cellular responses, including proliferation, growth, chemotaxis, and survival. These diverse effects can partly be attributed to the broad range of downstream effectors being regulated by the products of these lipid kinases, the 3 ¶-phosphoinositides. However, an additional layer of complexity is introduced by the existence of multiple PI3K enzyme isoforms. Much has been learned over the last years on the roles of the classes I and III PI3K members in cellular signaling, but little is known about the isoform-specific tasks done by the class II PI3Ks (C2A, B, and ;). In this study, we used quantitative reverse transcription -PCR and RNA interference in mammalian cells to gain further insight into the function of these lesser studied PI3K enzymes. We find that PI3K-C2A, but not PI3K-C2B, has an important role in controlling cell survival and by using a panel of RNA interference reagents, we were able to determine a critical threshold of PI3K-C2A mRNA levels, below which the apoptotic program is switched on, via the intrinsic cell death pathway. In addition, knockdown of PI3K-C2A to levels that by themselves do not induce apoptosis sensitize cells to the anticancer agent Taxol (paclitaxel). Lastly, we report that lowering the levels of PI3K-C2A in a number of cancer cell lines reduces their proliferation and cell viability, arguing that PI3K inhibitors targeting not only the class IA isoform but also class IIA may contribute to an effective anticancer strategy. (Mol Cancer Res 2008;6(4):614 -23)

Attenuation of the beta-catenin/TCF4 complex in colorectal cancer cells induces several growth-suppressive microRNAs that target cancer promoting genes

“…Fragments representing all three mRNAs were responsive with many fragments being highly efficient in mediating suppression by miR-30e-3p regardless of whether the fragment originated from the open reading frame or the 3 0 UTR (Figure 5c). Of the three targets, we decided to focus on HELZ and PIK3C2A because, unlike WDR44, they have previously been implicated in cellular growth control (Hamamoto et al, 2004;Elis et al, 2008;Ng et al, 2009). As a first step, we confirmed that the miR-30e-3p-mediated suppression of luciferase reporter activity was specific to this miRNA by showing that several other miRNAs, completely lacking seed-matched complementarity to the cloned sequences, were not able to impair luciferase reporter activity (Figure 5d).…”

“…Recent work has shown that PIK3C2A propagates growth stimuli in cancer cells from different tissues (Elis et al, 2008;Ng et al, 2009), and HELZ has indirectly been associated with proliferation by reportedly being part of a SMYD3-containing growth-promoting protein complex (Hamamoto et al, 2004). Hence, we entertained the possibility that decreased PIK3C2A and HELZ levels were causally involved in restricting cell growth by specifically silencing PIK3C2A and HELZ in DLD1 cells using small interfering RNAs.…”

PIK3C2A is a gene-specific target of microRNA-518a-5p in imatinib mesylate-resistant gastrointestinal stromal tumor

“…It is further documented that miR-518a-5p reduced 882R proliferation and promoted 882R apoptosis, and transfection of GIST cells with miR-518a-5p leads to significant PIK3C2A downregulation at the mRNA and protein level. PIK3C2A has been reported to promote tumor survival, 29,30 therefore, low expression of miR-518a-5p is likely to upregulate PIK3C2A and affect the cellular response to the drug, causing resistance to imatinib in GIST. Consequently, our findings may aid in the understanding of miRNA gene regulation with respect to PIK3C2A and their interaction in GIST cells, emphasizing the importance of further studies of the regulative mechanism underlying the miR-518a-5p/PIK3C2A interaction.…”

Requirement for Class II Phosphoinositide 3-Kinase C2α in Maintenance of Glomerular Structure and Function

“…Selective engagement of PI3K-p85 by nephrin and CD2AP is known to promote phosphorylation of AKT, which serves as a potent antiapoptotic regulator protecting podocytes from cell death (23). Similarly, inhibition of PI3KC2␣ expression is associated with increased susceptibility to apoptosis and decreased proliferative capacity in various cell types (15,35). Increased expression of the proapoptotic cytokine transforming growth factor ␤ (TGF-␤) has been observed in CD2AP-deficient mice (41).…”

“…PI3KC2␣ may also play a role in regulating cell survival. For instance, RNA interference (RNAi)-mediated knockdown of PI3KC2␣ expression induced apoptosis via an intrinsic cell death pathway in HeLa (15) and CHO (26) cells, which was associated with increased levels of activated caspase 9 (15). Data from other recent studies have provided evidence that PI3KC2␣ is a component of diverse cellular processes ranging from neurosecretory granule exocytosis (50) and vascular smooth muscle contraction (53) to insulin signaling (18).…”