HTRA4 and lung carcinoma: Since it has been previously shown that localization of the HtrA1-3 proteins depends on the presence or absence of their N-terminal domains [29,30,32,33], we used the lung cancer cells (A549) with exogenous expression of the full-length HtrA4 or of its N-terminally truncated variant, called ΔN-HtrA4, both tagged with the GFP protein as a fluorescent marker.