Primary tumors facilitate metastasis by directing bone marrowderived cells (BMDCs) to colonize the lungs before the arrival of cancer cells. Here, we demonstrate that hypoxia-inducible factor 1 (HIF-1) is a critical regulator of breast cancer metastatic niche formation through induction of multiple members of the lysyl oxidase (LOX) family, including LOX, LOX-like 2, and LOX-like 4, which catalyze collagen cross-linking in the lungs before BMDC recruitment. Only a subset of LOX family members was expressed in any individual breast cancer, but HIF-1 was required for expression in each case. Knockdown of HIF-1 or hypoxia-induced LOX family members reduced collagen cross-linking, CD11b+ BMDC recruitment, and metastasis formation in the lungs of mice after orthotopic transplantation of human breast cancer cells. Metastatic niche formation is an HIF-1-dependent event during breast cancer progression. extracellular matrix | lung metastasis I ntratumoral hypoxia is a common finding that is attributable to inadequate O 2 delivery to regions of rapidly growing cancers that are distant from functional blood vessels (1). Reduced O 2 availability leads to increased activity of hypoxia-inducible factors (HIFs), which consist of an O 2 -regulated HIF-1α or HIF-2α subunit and the constitutively expressed HIF-1β subunit (2, 3). HIF inhibition blocks tumor xenograft growth (2, 4).Metastasis is responsible for 90% of deaths among patients who have breast cancer and involves multiple steps, including cancer cell invasion through ECM, intravasation, extravasation, and colonization of distant organs (5). Recent studies have reported that prior recruitment of bone marrow-derived cells (BMDCs) to the metastatic site promotes subsequent colonization by cancer cells (6). The primary tumor is responsible for BMDC recruitment to the metastatic site. Breast tumors secrete lysyl oxidase (LOX), which localizes at metastatic sites in the lungs and remodels collagen, thereby facilitating BMDC recruitment (7,8). LOX oxidatively deaminates the ε-amino groups of lysine residues, resulting in intramolecular and intermolecular cross-linking of collagen molecules (9). Crosslinking stabilizes collagen by assembly into fibrils and fibers, which enhance ECM tensile strength, leading to focal adhesion formation and PI3K signaling (10). The LOX family is composed of LOX and LOX-like (LOXL) proteins LOXL1-4. So far, only LOX has been implicated in metastatic niche formation (7). In this study, we demonstrate that HIF-1 regulates metastatic niche formation by activating expression of LOX and LOXL proteins. HIF-1 silencing suppresses metastatic niche formation and metastasis regardless of which LOX family member is involved. ResultsHypoxia-Induced LOX/LOXL Expression in Breast Cancer Cell Lines.Two metastatic breast cancer cell lines, MDA-MB-231 (MDA-231) and MDA-MB-435 (MDA-435), as well as a nonmetastatic line, MCF-7, were cultured under standard, nonhypoxic tissue culture conditions of 95% air/5% CO 2 (vol/vol; 20% O 2 ) and under hypoxic culture conditi...

FOXM1 has been implicated in taxane resistance, but the molecular mechanism involved remains elusive. In here, we show that FOXM1 depletion can sensitize breast cancer cells and mouse embryonic fibroblasts into entering paclitaxel-induced senescence, with the loss of clonogenic ability, and the induction of senescence-associated β-galactosidase activity and flat cell morphology. We also demonstrate that FOXM1 regulates the expression of the microtubulin-associated kinesin KIF20A at the transcriptional level directly through a Forkhead response element (FHRE) in its promoter. Similar to FOXM1, KIF20A expression is downregulated by paclitaxel in the sensitive MCF-7 breast cancer cells and deregulated in the paclitaxel-resistant MCF-7TaxR cells. KIF20A depletion also renders MCF-7 and MCF-7TaxR cells more sensitive to paclitaxel-induced cellular senescence. Crucially, resembling paclitaxel treatment, silencing of FOXM1 and KIF20A similarly promotes abnormal mitotic spindle morphology and chromosome alignment, which have been shown to induce mitotic catastrophe-dependent senescence. The physiological relevance of the regulation of KIF20A by FOXM1 is further highlighted by the strong and significant correlations between FOXM1 and KIF20A expression in breast cancer patient samples. Statistical analysis reveals that both FOXM1 and KIF20A protein and mRNA expression significantly associates with poor survival, consistent with a role of FOXM1 and KIF20A in paclitaxel action and resistance. Collectively, our findings suggest that paclitaxel targets the FOXM1-KIF20A axis to drive abnormal mitotic spindle formation and mitotic catastrophe and that deregulated FOXM1 and KIF20A expression may confer paclitaxel resistance. These findings provide insights into the underlying mechanisms of paclitaxel resistance and have implications for the development of predictive biomarkers and novel chemotherapeutic strategies for paclitaxel resistance.

Severe acute respiratory syndrome (SARS) is caused by infection of a previously undescribed coronavirus (CoV). L-SIGN, encoded by CLEC4M (also known as CD209L), is a SARS-CoV binding receptor that has polymorphism in its extracellular neck region encoded by the tandem repeat domain in exon 4. Our genetic risk association study shows that individuals homozygous for CLEC4M tandem repeats are less susceptible to SARS infection. L-SIGN is expressed in both non-SARS and SARS-CoV-infected lung. Compared with cells heterozygous for L-SIGN, cells homozygous for L-SIGN show higher binding capacity for SARS-CoV, higher proteasome-dependent viral degradation and a lower capacity for trans infection. Thus, homozygosity for L-SIGN plays a protective role during SARS infection.