Inhibition of Proprotein Convertases Enhances Cell Migration and Metastases Development of Human Colon Carcinoma Cells in a Rat Model

Abstract

Although proprotein convertases are involved in tumor development, nothing is known about their role in metastatic dissemination. To investigate the involvement of convertase inhibition, we used human colon carcinoma cells overexpressing ␣1-antitrypsin Portland (␣1-PDX, PDX39P cells), a potent convertase inhibitor. We previously reported that these cells bear uncleaved integrin ␣ subunits and display an altered attachment to vitronectin that is correlated with defects in the intracellular signaling pathways activated by ␣v␤5 integrin ligation. In this study, we demonstrate that the inhibition of proprotein convertase activity either by overexpression of ␣1-PDX or with the synthetic inhibitor decanoyl-Arg-Val-Lys-Arg-chloromethylketone (dec-RVKR-cmk) led to a significant increase in cell migration supported by the ␣v␤5 integrin. A collagen gel invasion assay showed that PDX39P cells also displayed an invasive ability, contrary to control cells. Moreover, when injected to immunosuppressed newborn rats, PDX39P cells were highly invasive, as they induce 10 times more metastases than mock-transfected cells. In addition, the aggressiveness of PDX39P cells can be greatly reduced by a function-blocking monoclonal antibody (mAb) against the ␣v subunit. It thus seems that inhibition of proprotein convertases enhances the in vivo invasiveness of colon tumor cells likely due to an increase in cell migration mediated by ␣v integrins. The acquisition of cell motility and the capacity to invade basement matrix membranes and adjacent tissues play a central role in the complex multi-step process of metastasis. Cell migration is the result of dynamic interactions between the cell, the extracellular matrix (ECM), and the cytoskeleton. Integrins connect the ECM proteins outside to the actin cytoskeleton within the cell, allowing the traction required for cell migration. 1,2 Integrins also play a crucial role in signal transduction events that control anchorage-independent growth and survival of tumor cells (for reviews, see references [3][4][5] ). Therefore, these adhesion molecules play a pivotal role in tumor cell invasion and metastasis. [5][6][7] Integrins are heterodimeric proteins composed by the non-covalent association of ␣ and ␤ subunits. Some integrin ␣ chains undergo a post-translational cleavage in their extracellular domain by furin and PC5A, two proprotein convertases (PCs) of the subtilisin/kexin family. 8,9 The role of this cleavage in integrin function remains unclear. Arguably, this post-translational processing of the ␣ chain is not required for ligand binding, 10 -12 but is essential for the signaling function of ␣6␤1 and ␣v␤5 integrins. 10,13 Moreover, recent data suggest that the ␣6 subunit cleavage might be linked to the differentiation state of lens cells. 14 PCs are responsible for the biological activation of a variety of precursor proteins, including pro-hormones and their receptors and adhesion molecules. They are ubiquitously expressed and are involved in many physiological and pathological processes. ...

Opposing Function of the Proprotein Convertases Furin and PACE4 on Breast Cancer Cells' Malignant Phenotypes: Role of Tissue Inhibitors of Metalloproteinase-1

“…Earlier reports showed that a1-PDX overexpression in different tumor cell systems resulted in a reduced invasiveness and in vivo tumorigenicity in nude mice (2,8,16). In other studies, this inhibitor was found to increase cell migration and accelerate the process of metastasis (17). Accordingly, overexpression of Furin has been established in various types of cancers (2,10,14) and has been linked to aggressive behavior in some model systems (14).…”

“…Student's t test was used for statistical analysis. *, P < 0.05; **, P < 0.01; ***, P < 0.001. expressed in various cancers (10,(14)(15)(16)(17). Earlier reports showed that a1-PDX overexpression in different tumor cell systems resulted in a reduced invasiveness and in vivo tumorigenicity in nude mice (2,8,16).…”

Lebectin and lebecetin, two C-type lectins from snake venom, inhibit α5β1 and αv-containing integrins

“…However, the α5 and αv subunits belong to a second subset of α integrin subunits lacking the I domain. They instead undergo an endoproteolytic cleavage that is essential for integrin function Nejjari et al, 2004). Ligation of α5β1 and αvβ3 integrins also leads to conformational changes that are propagated all along the molecule (Takagi et al, 2001;Takagi et al, 2002).…”

Can Alpha-1 Antitrypsin be Involved in the Carcinogenesis of Colorectal Cancer?

“…This same mechanism would possibly be shared by all other types of cancers, including CRC. It is known that both normal and cancer intestinal cells secrete AAT to neutralize elastase [22], which is present in high concentrations in CRC cells, in an attempt to maintain the proteaseantiprotease balance, preventing the activation of procathepsin B and proprotein convertase, and reducing production of Tumor Necrosis Factor (TNF) alpha, and Interleukin-1a, which in turn prevents liver metastases [23][24][25]. There is also some evidence of a relationship between AAT deficiency and the development of neoplasms of the urinary bladder, gallbladder, and malignant lymphomas [12][13][14].…”