LAMPs: Shedding light on cancer biology

Lysosomes are important cytoplasmic organelles whose critical functions in cells are increasingly being understood. In particular, despite the long-standing accepted concept about the role of lysosomes as cellular machineries solely assigned to degradation, it has been demonstrated that they play active roles in homeostasis and even in cancer biology. Indeed, it is now well documented that during the process of cellular transformation and cancer progression lysosomes are changing localization, composition, and volume and, through the release of their enzymes, lysosomes can also enhance cancer aggressiveness. LAMPs (lysosome associated membrane proteins) represent a family of glycosylated proteins present predominantly on the membrane of lysosomes whose expression can vary among different tissues, suggesting a separation of functions. In this review we focus on the functions and roles of the different LAMP family members, with a particular emphasis on cancer progression and metastatic spread. LAMP proteins are involved in many different aspects of cell biology and can influence cellular processes such as phagocytosis, autophagy, lipid transport, and aging. Interestingly, for all the five members identified so far (LAMP1, LAMP2, LAMP3, CD68/Macrosialin/LAMP4, and BAD-LAMP/LAMP5), a role in cancer has been suggested. While this is well documented for LAMP1 and LAMP2, the involvement of the other three proteins in cancer progression and aggressiveness has recently been proposed and remains to be elucidated. Here we present different examples about how LAMP proteins can influence and support tumor growth and metastatic spread, emphasizing the impact of each single member of the family.