Low molecular weight hyaluronan (LMW‐HA), a degradation fragment of the extracellular matrix component hyaluronan (HA), has been proven to play a crucial role in cancer progression. However, no systematic clinical study of breast cancer has been performed to correlate LMW‐HA levels with metastasis. In the present study, we analyzed 176 serum specimens and found for the first time that the serum LMW‐HA (but not total HA) level significantly correlated with lymph node metastasis, suggesting that serum LMW‐HA represents a better prognostic indicator of breast cancer progression than HA. Similarly, we found that breast cancer cell lines displaying higher invasive potential had a higher LMW‐HA concentration than less‐invasive cell lines. This higher LMW‐HA level was accompanied by the overexpression of hyaluronan synthase (HAS2) and hyaluronidase (both HYAL1 and HYAL2). Of great importance, decreasing LMW‐HA production significantly inhibited breast cancer cell migration and invasion. Overall, our results suggest that during cancer progression, cancer cells may actively remodel their microenvironment via an autocrine/paracrine‐like process, resulting in elevated LMW‐HA levels, which in turn may facilitate cancer progression by promoting the migration and invasion of cancer cells. Therefore, cancer‐associated LMW‐HA may be a more promising molecular biomarker than total HA for detecting metastasis and may have further applications in breast cancer treatment.—Wu, M., Cao, M., He, Y., Liu, Y., Yang, C., Du, Y., Wang, W., Gao, F. A novel role of low molecular weight hyaluronan in breast cancer metastasis. FASEB J. 29, 1290‐1298 (2015). www.fasebj.org

CD44, a non‐kinase transmembrane glycoprotein, is ubiquitously expressed on various types of cells, especially cancer stem cells (CSCs), and has been implicated in cancer onset and aggressiveness. The major ligand for the CD44, hyaluronan (HA), binds to and interacts with CD44, which in turn triggers downstream signaling cascades, thereby promoting cellular behaviors such as proliferation, motility, invasiveness and chemoresistance. The CD44‐HA interaction is cell‐specific and strongly affected by the state of CD44 activation. Therefore, the binding of HA to CD44 is essential for the activation of CD44 during which the detailed regulatory mechanism needs to be clarified. Different CD44 activation states distribute in human carcinoma and normal tissue; however, whether CD44 activation is a critical requirement for tumor initiation, progression and notorious CSC properties remains to be clarified. A deeper understanding of the regulation of CD44 activation may facilitate the development of novel targeted drugs in the future. Here, we review the current findings concerning the states of CD44 activation on the cell surface, the underlying regulatory mechanisms of CD44 activation, the known role for CD44 activation in tumor progression and CSC hallmarks, as well as the potential of HA‐coated nanoparticle for targeting activated CD44 for cancer therapy.

Hyaluronan (HA), a large nonsulfated glycosaminogycan in the extracellular matrix, whose degraded fragments termed as low molecular weight hyaluronan (LMW-HA), has been reported as an important regulator of angiogenesis. However, little is known about the influence of LMW-HA on lymphangiogenesis. In this study, we try to explore the in vitro effects of LMW-HA on lymphangiogenesis and identify the underlying molecular mechanisms. Our results showed that LMW-HA stimulation significantly increased lymphatic endothelial cells (LECs) proliferation, migration and tube formation. Further experiments demonstrated that LMW-HA altered actin cytoskeleton rearrangement and increased the formation of intense stress fibers, lamellipodia and filopodia. Mechanistically, LMW-HA stimulation resulted in rapid tyrosine phosphorylation of protein kinase C α/βII (PKCα/βII) and extracellular-regulated kinase 1/2 (ERK1/2). Lymphalic vessel endotheilial hyaluronan receptor 1 (LYVE-1), a homologue of CD44, is the main cell surface receptor for HA in LECs. Blocking the binding interaction of LMW-HA with LYVE-1 using neutralizing anti-LYVE-1 antibodies significantly inhibited LECs proliferation, migration, tube formation and signal transduction induced by LMW-HA, suggesting that LMW-HA may play a critical role in the processes required for lymphangiogenesis through interactions with its receptor LYVE-1 and triggering intracellular signal cascades.

Microenvironmental signals determine the differentiation types and distinct functions of macrophages. Tumor-associated macrophages (TAM) constitute major infiltrates around solid tumor cells and accelerate tumor progression due to their immunosuppressive functions. However, the mechanisms through which tumor microenvironment modulates macrophages transition are not completely elucidated. Hyaluronan (HA), a prominent component in tumor microenvironment, is a notable immunoregulator and its high level is often related to poor prognosis. Herein, we found that the number of M2 macrophages was highly correlated with HA expression in tumor tissues from breast cancer patients. Experimental data showed that breast cancer-derived HA stimulated M2-like TAM formation in a mouse model and had multiple effects on macrophages transformation in vitro, including upregulating CD204, CD206, IL-10 and TGF-β, activating STAT3 signal, and suppressing killing capacity. These data indicate that HA derived from breast cancer activates macrophages in an alternative manner. Further mechanism study revealed that HA-CD44-ERK1/2-STAT3 pathway served as an important regulator in M2-like TAM formation. Therefore, targeting TAM by abrogating HA–CD44 interaction may be a potential strategy for breast cancer immunotherapy.