Banuelos Allison, Baez Michelle, Zhang Allison, Yılmaz Leyla, Kasberg William, Volk Regan, Georgeos Nardin, Koren-Sedova Elle, Le Uyen, Burden Andrew T, Marjon Kristopher D, Lippincott-Schwartz Jennifer, Zaro Balyn W, Weissman Irving L
Institute for Stem Cell Biology and Regenerative Medicine, Stanford University School of Medicine, Stanford, CA 94305.
Ludwig Center for Cancer Stem Cell Research and Medicine, Stanford University School of Medicine, Stanford, CA 94305.
Proc Natl Acad Sci U S A. 2025 May 27;122(21):e2426644122. doi: 10.1073/pnas.2426644122. Epub 2025 May 21.
Calreticulin (CALR) is primarily an endoplasmic reticulum chaperone protein that also plays a key role in facilitating programmed cell removal (PrCR) by acting as an "eat-me" signal for macrophages, directing their recognition and engulfment of dying, diseased, or unwanted cells. Recent findings have demonstrated that macrophages can transfer their own CALR onto exposed asialoglycans on target cells, marking them for PrCR. Despite the critical role CALR plays in this process, the molecular mechanisms behind its secretion by macrophages and the formation of binding sites on target cells remain unclear. Our findings show that CALR undergoes C-terminal cleavage upon secretion, producing a truncated form that functions as the active eat-me signal detectable on target cells. We identify cathepsins as potential proteases involved in this cleavage process. Furthermore, we demonstrate that macrophages release neuraminidases, which modify the surface of target cells and facilitate CALR binding. These insights reveal a coordinated mechanism through which lipopolysaccharide (LPS)-activated macrophages regulate CALR cleavage and neuraminidase activity to mark target cells for PrCR. How they recognize the cells to be targeted remains unknown.
钙网蛋白（CALR）主要是一种内质网伴侣蛋白，它还通过作为巨噬细胞的“吃我”信号，在促进程序性细胞清除（PrCR）中发挥关键作用，引导巨噬细胞识别和吞噬垂死、患病或不需要的细胞。最近的研究结果表明，巨噬细胞可以将自身的CALR转移到靶细胞上暴露的去唾液酸糖蛋白上，标记这些细胞以便进行PrCR。尽管CALR在这一过程中起着关键作用，但其由巨噬细胞分泌以及在靶细胞上形成结合位点背后的分子机制仍不清楚。我们的研究结果表明，CALR在分泌时会发生C端切割，产生一种截短形式，其作为可在靶细胞上检测到的活性“吃我”信号发挥作用。我们确定组织蛋白酶是参与这一切割过程的潜在蛋白酶。此外，我们证明巨噬细胞会释放神经氨酸酶，这些酶会修饰靶细胞表面并促进CALR结合。这些见解揭示了一种协调机制，通过该机制脂多糖（LPS）激活的巨噬细胞调节CALR切割和神经氨酸酶活性，以标记靶细胞进行PrCR。它们如何识别要靶向的细胞仍然未知。
