LC3s (MAP1-LC3A, B and C) are structural proteins of autophagosomal membranes, widely used as biomarkers of autophagy. Whether these three LC3 proteins have a similar biological role in autophagy remains obscure. We examine in parallel the subcellular expression patterns of the three LC3 proteins in a panel of human cancer cell lines, as well as in normal MRC5 fibroblasts and HUVEC, using confocal microscopy and western blot analysis of cell fractions. In the cytoplasm, there was a minimal co-localization between LC3A, B and C staining, suggesting that the relevant autophagosomes are formed by only one out of the three LC3 proteins. LC3A showed a perinuclear and nuclear localization, while LC3B was equally distributed throughout the cytoplasm and localized in the nucleolar regions. LC3C was located in the cytoplasm and strongly in the nuclei (excluding nucleoli), where it extensively co-localized with the LC3A and the Beclin-1 autophagy initiating protein. Beclin 1 is known to contain a nuclear trafficking signal. Blocking nuclear export function by Leptomycin B resulted in nuclear accumulation of all LC3 and Beclin-1 proteins, while Ivermectin that blocks nuclear import showed reduction of accumulation, but not in all cell lines. Since endogenous LC3 proteins are used as major markers of autophagy in clinical studies and cell lines, it is essential to check the specificity of the antibodies used, as the kinetics of these molecules are not identical and may have distinct biological roles. The distinct subcellular expression patterns of LC3s provide a basis for further studies.

Glioblastoma cells are resistant to apoptotic stimuli with autophagic death prevailing under cytotoxic stress. Autophagy interfering agents may represent a new strategy to test in combination with chemo-radiation. We investigated the patterns of expression of autophagy related proteins (LC3A, LC3B, p62, Beclin 1, ULK1 and ULK2) in a series of patients treated with post-operative radiotherapy. Experiments with glioblastoma cell lines (T98 and U87) were also performed to assess autophagic response under conditions simulating the adverse intratumoral environment. Glioblastomas showed cytoplasmic overexpression of autophagic proteins in a varying extent, so that cases could be grouped into low and high expression groups. 10/23, 5/23, 13/23, 5/23, 8/23 and 9/23 cases examined showed extensive expression of LC3A, LC3B, Beclin 1, Ulk 1, Ulk 2 and p62, respectively. Lysosomal markers Cathepsin D and LAMP2a, as well as the lyososomal biogenesis transcription factor TFEB were frequently overexpressed in glioblastomas (10/23, 11/23, and 10/23 cases, respectively). TFEB was directly linked with PTEN, Cathepsin D, HIF1α, LC3B, Beclin 1 and p62 expression. PTEN was also significantly related with LC3B but not LC3A expression, in both immunohistochemistry and gene expression analysis. Confocal microscopy in T98 and U87 cell lines showed distinct identity of LC3A and LC3B autophagosomes. The previously reported stone-like structure (SLS) pattern of LC3 expression was related with prognosis. SLS were inducible in glioblastoma cell lines under exposure to acidic conditions and 2DG mediated glucose antagonism. The present study provides the basis for autophagic characterization of human glioblastoma for further translational studies and targeted therapy trials.

Glioblastoma is a unique model of non-metastasising disease that kills the vast majority of patients through local growth, despite surgery and local irradiation. Glioblastoma cells are resistant to apoptotic stimuli, and their death occurs through autophagy. This review aims to critically present our knowledge regarding the autophagic response of glioblastoma cells to radiation and temozolomide (TMZ) and to delineate eventual research directions to follow, in the quest of improving the curability of this incurable, as yet, disease. Radiation and TMZ interfere with the autophagic machinery, but whether cell response is driven to autophagy flux acceleration or blockage is disputable and may depend on both cell individuality and radiotherapy fractionation or TMZ schedules. Potent agents that block autophagy at an early phase of initiation or at a late phase of autolysosomal fusion are available aside to agents that induce functional autophagy, or even demethylating agents that may unblock the function of autophagy-initiating genes in a subset of tumours. All these create a maze, which if properly investigated can open new insights for the application of novel radio- and chemosensitising policies, exploiting the autophagic pathways that glioblastomas use to escape death.

Cooperation of cancer cells with stromal cells, such as cancer-associated fibroblasts (CAFs), has been revealed as a mechanism sustaining cancer cell survival and growth. In the current study, we focus on the metabolic interactions of MRC5 lung fibroblasts with lung cancer cells (A549 and H1299) using co-culture experiments and studying changes of the metabolic protein expression profile and of their growth and migration abilities. Using western blotting, confocal microscopy and RT-PCR, we observed that in co-cultures MRC5 respond by upregulating pyruvate dehydrogenase (PDH) and the monocarboxylate transporter MCT1. In contrast, cancer cells increase the expression of glucose transporters (GLUT1), LDH5, PDH kinase and the levels of phosphorylated/inactivated pPDH. H1299 cells growing in the same culture medium with fibroblasts exhibit a 'metastasis-like' phenomenon by forming nests within the fibroblast area. LDH5 and pPDH were drastically upregulated in these nests. The growth rate of both MRC5 and cancer cells increased in co-cultures. Suppression of LDHA or PDK1 in cancer cells abrogates the stimulatory signal from cancer cells to fibroblasts. Incubation of MRC5 fibroblasts with lactate resulted in an increase of LDHB and of PDH expression. Silencing of PDH gene in fibroblasts, or silencing of PDK1 or LDHA gene in tumor cells, impedes cancer cell's migration ability. Overall, a metabolic cooperation between lung cancer cells and fibroblasts has been confirmed in the context of direct Warburg effect, thus the fibroblasts reinforce aerobic metabolism to support the intensified anaerobic glycolytic pathways exploited by cancer cells.