Netrin-1 expression confers a selective advantage for tumor cell survival in metastatic breast cancer

Abstract

Netrin-1, an axon navigation cue was proposed to play a crucial role during colorectal tumorigenesis by regulating apoptosis. The netrin-1 receptors DCC and UNC5H were shown to belong to the family of dependence receptors that share the ability to induce apoptosis in the absence of their ligands. Such a trait confers on these receptors a tumor suppressor activity. Expression of one of these dependence receptors at the surface of a tumor cell is indeed speculated to render this cell dependent on ligand availability for its survival, hence inhibiting uncontrolled cell proliferation or metastasis. Consequently, it is a selective advantage for a tumor cell to lose this dependence receptor activity, as previously described with losses of DCC and UNC5H expression in human cancers. However, the model predicts that a similar advantage may be obtained by gaining autocrine expression of the ligand. We describe here that, unlike human nonmetastatic breast tumors, a large fraction of metastatic breast cancers overexpress netrin-1. Moreover, we show that netrin-1-expressing mammary metastatic tumor cell lines undergo apoptosis when netrin-1 expression is experimentally decreased or when decoy soluble receptor ectodomains are added. Such treatments prevent metastasis formation both in a syngenic mouse model of lung colonization of a mammary cancer cell line and in a model of spontaneous lung metastasis of xenografted human breast tumor. Thus, netrin-1 expression observed in a large fraction of human metastatic breast tumors confers a selective advantage for tumor cell survival and potentially represents a promising target for alternative anticancer therapeutic strategies.apoptosis ͉ DCC ͉ dependence receptor N etrin-1, a diffusible laminin-related protein, has been shown to play a major role in the control of neuronal navigation during the development of the nervous system by interacting with its main receptors, DCC (Deleted in Colorectal Cancer) (1-3) and UNC5H (4, 5). However, more recently, netrin-1 has emerged as a completely different molecule that regulates cell survival. Indeed, the netrin-1 receptors DCC and UNC5H, i.e., UNC5H1, UNC5H2, and UNC5H3, belong to the so-called dependence receptor family (6, 7). Such receptors share the functional property of inducing cell death when disengaged from their ligands, whereas the presence of their ligands blocks this proapoptotic activity. Such receptors thus create cellular states of dependence on their respective ligands (8,9).This dependence effect has been suggested to act as a mechanism for eliminating tumor cells that would develop in settings of ligand unavailability: proliferation of tumor cells in a cell environment with constant and limited ligand presence or migration of metastatic tumor cells toward tissues where the ligand is not expressed. A selective advantage for a tumor cell would then be to lose the proapoptotic activity of its dependence receptors. Along this line, DCC was proposed in the early 1990s to be a tumor-suppressor gene, whose expression is lost in ...

Kremen1 and Dickkopf1 control cell survival in a Wnt-independent manner

“…New perspectives are currently arising, consisting in characterizing tumors that express both a dependence receptor and its ligand and trying to interfere with production of the latter. [38][39][40][41] We provide strong evidences supporting an evolutionary acquisition of dependence behavior for Krm1, which might be one of the mechanisms by which placental mammals tackled the necessity to develop protective strategies against cancers. We further suggest that in humans, Krm1 apoptotic behavior can be regulated by alternative splicing.…”

Dependence receptors: a new paradigm in cell signaling and cancer therapy

“…Whereas restoring the expression of an extinguished receptorcoding gene does not seem conceivable, interfering with ligand binding seems to be a more pertinent approach, further supported by recent studies reporting an overexpression of netrin-1 in various cancers (Link et al, 2007;Fitamant et al, 2008;Delloye-Bourgeois et al, 2009a, b). These studies provide an idea of what the future therapeutic molecules used in clinical studies could be; for example, a decoy receptor corresponding to the entire ectodomain of DCC receptor that would titrate the ligand, thus leading to unbound membrane receptors (Fitamant et al, 2008). However, the large size (1100 aa) of the complete extracellular domain of DCC may complicate its use in vivo.…”

“…More recently, high levels of netrin-1 were detected in a large panel of human cancers from distinct organs, and netrin-1 overexpression was correlated with a blocking of the proapoptotic functions of netrin-1 receptors. First, in breast cancer, netrin-1 was shown to be a marker of metastatic disease: decrease in netrin-1 expression by small interfering RNA or netrin-1 titration by decoy soluble receptor ectodomain causes apoptosis and prevents metastasis formation both in a syngenic mouse model and in a xenograft model (Fitamant et al, 2008). In the same way, high levels of netrin-1 were detected in almost 50% of non-small-cell lung cancer and in a large fraction of aggressive neuroblastoma.…”

“…However, the large size (1100 aa) of the complete extracellular domain of DCC may complicate its use in vivo. An alternative could be to use shorter polypeptides, corresponding to the fourth or fifth fibronectin-like domain of DCC (Fitamant et al, 2008;Delloye-Bourgeois et al, 2009a, b), which are both known to interact with netrin-1 (Geisbrecht et al, 2003). Unlike the complete ectodomain, the fifth and fourth fibronectin-like domains do not counteract interaction between netrin-1 and its receptors, but rather block receptor multimerization (Mille et al, 2009a).…”

Netrin-1, a missing link between chronic inflammation and tumor progression

“…7 In the same line, a netrin-1 gain has recently been described in several human cancers, such as colorectal cancer, 22,23 metastatic breast cancers, 24 lung cancer, 25 and neuroblastoma 26 and this netrin-1 overexpression has been shown as a selective advantage for tumor progression. [23][24][25][26] The netrin-1/dependence receptors pair represents therefore a relevant mechanism to control tumor development and cellular escape. While several evidences show that, at genetic or epigenetic level, the downregulation of dependence receptor expression occurs through loss of heterozygosity or promoter methylation, 17,20,27 the mechanism allowing netrin-1 upregulation is not completely understood.…”