Phosphatidylinositol Phosphate 5-Kinase Iγi2 in Association with Src Controls Anchorage-independent Growth of Tumor Cells

Abstract

Background: PIPKI␥ isoforms play roles in cell migration, polarization, and membrane trafficking and are overexpressed in triple-negative breast cancers, indicating protumorigenic functions. Results: PIPKI␥i2 associates with the C terminus of Src, and this interaction interdependently controls their functioning. Conclusion: PIPKI␥i2 and Src synergistically control anchorage-independent tumor cell growth. Significance: This study shows unexpected mechanisms for a phosphatidylinositol 4,5-biphosphate-generating enzyme that synergizes with the proto-oncogene Src to regulate oncogenic signaling.

Phosphatidylinositol Phosphate 5-Kinase Iγ and Phosphoinositide 3-Kinase/Akt Signaling Couple to Promote Oncogenic Growth

“…As shown in Fig. 2, E and F, PIPKI␥ knockdown significantly abrogated the activation level of Akt in the suspension culture of T47D and Cal51 cells and is consistent with the impaired anchorage-independent growth of these tumor cells upon PIPKI␥ loss (18).…”

“…Anchorage-independent Growth-For anchorage-independent growth, cells were suspended into the medium containing 0.3% agar and seeded into 24-well culture plates (18). To avoid cell attachment, culture plates were precoated with 0.5% agar before cell seeding.…”

“…DNA Constructs and siRNA-DNA constructs used in the study were described previously (18,22). siRNA oligonucleotides used were as follows: control siRNA, CCUUGGUGACUCGUAGUUU; siPIPKI␥i2, GAGCGACACAUAAUUUCUA; siPIPKI␥i5, GGA-UGGGAGGUACUGGAUU; siPIPKI␥, GCCACCTTCTTTC-GAAGAA; siPIPKI␣, GAAGUUGGAGCACUCUUGG; siSrc, GGCUCCAGAUUGUCAACAA and GCCUCAACGUG-AAGCACUA.…”

“…1C). Because PIPKI␥ is overexpressed in triplenegative breast cancer tissues and plays a role in anchorageindependent growth of tumor cells (18,26), its role in PI3K/Akt signaling was further examined. The effect of PIPKI␥ knockdown on the time course of Akt activation after FBS or ECM stimulation of MDA-MB-231 cells was examined (Fig.…”

“…Src phosphorylation of PIPKI␥i2 regulates its interaction with talin and its targeting to focal adhesion sites (17). Furthermore, Src and PIPKI␥i2 are directly interacting partners, both required for oncogenic growth of tumor cells (18). Recently, PIPKI␥ has been shown to modulate breast cancer metastasis, although the specific isoforms involved were not defined (19).…”