Inhibition of metastasis by HEXIM1 through effects on cell invasion and angiogenesis

Abstract

We report on the role of Hexamethylene-bis-acetamide-inducible protein 1 (HEXIM1) as an inhibitor of metastasis. HEXIM1 expression is decreased in human metastatic breast cancers when compared to matched primary breast tumors. Similarly we observed decreased expression of HEXIM1 in lung metastasis when compared to primary mammary tumors in a mouse model of metastatic breast cancer, the Polyoma Middle-T antigen (PyMT) transgenic mouse. Re-expression of HEXIM1 (through transgene expression or localized delivery of a small molecule inducer of HEXIM1 expression, Hexamethylene-bis-acetamide) in PyMT mice resulted in inhibition of metastasis to the lung. Our present studies indicate that HEXIM1 downregulation of HIF-1α protein allows not only for inhibition of VEGF-regulated angiogenesis, but also inhibition of compensatory pro-angiogenic pathways and recruitment of bone marrow derived cells (BMDCs). Another novel finding is that HEXIM1 inhibits cell migration and invasion, that can be partly attributed to decreased membrane localization of the 67kDa laminin receptor, 67LR, and inhibition of the functional interaction of 67LR with laminin. Thus HEXIM1 re-expression in breast cancer has therapeutic advantages by simultaneously targeting more than one pathway involved in angiogenesis and metastasis. Our results also support the potential for HEXIM1 to indirectly act on multiple cell types to suppress metastatic cancer.

Down-regulation of hypoxia-inducible factor-1 alpha and vascular endothelial growth factor by HEXIM1 attenuates myocardial angiogenesis in hypoxic mice

“…There have been pros and cons in the relationship between HEXIM1 and HIF-1a. In line with our results, the levels of HIF-1a protein was reported to be increased in HEXIM1+/À heterozygous hearts subjected ischaemic stress and that down-regulation of HIF-1a protein by HEXIM1 allows not only for inhibition of VEGF-regulated angiogenesis, but also for inhibition of migration and invasion of breast cancer cells [18,31]. Recently, HEXIM1 was shown to down-regulate HIF-1a protein stability by direct interaction with HIF-1a and up-regulation of hydroxylation of HIF-1a, resulting in the induction of the interaction of HIF-1a with pVHL (von Hippel-Lindau protein) and ubiquitination of HIF-1a [19].…”

“…Recently, HEXIM1 has been shown as an inhibitor of tumor angiogenesis via down-regulation of HIF-1a protein expression and inhibition of HIF-1a-mediated transcription [17,18]. The mechanistic basis for regulation of HIF-1a by HEXIM1 has been considered that HEXIM1 down-regulates HIF-1a protein stability [19].…”

RNA Polymerase II Transcription Elongation Control

“…184 Underexpression of HEXIM1 is associated with metastatic breast cancers and subsequent induction leads to an inhibition of metastasis. 185 The effects of HEXIM proteins are widespread in the animal kingdom. Global knockdown of Drosophila HEXIM is embryonic lethal and tissue specific knockdown severely impacts the development of all organs examined.…”

HEXIM1 down-regulates hypoxia-inducible factor-1α protein stability

“…HEXIM1 expression was induced in mammary epithelial cells of PyMT (Polyoma Middle-T antigen) mice by mating MMTV/HEXIM1 bitransgenic mice with PyMT mice as described previously [14]. HEXIM1 expression was induced by supplementing the drinking water of mice with doxycycline at a final concentration of 2 mg/ml.…”

“…We have recently reported that re-expression of HMBA (hexamethylene-bis-acetamide)-inducible protein 1 HEXIM1 through transgene expression or polymer-mediated delivery of HMBA inhibited metastasis in a mouse model of metastatic mammary cancer that can be correlated with decreased expression of HIF-1 α , VEGF, compensatory pro-angiogenic factors and vascularization [14]. We now report that HEXIM1 directly regulates HIF-1 α protein stability by up-regulating hydroxylation, interaction with pVHL and ubiquitination of HIF-1 α .…”