An emotional subject for Cassavetes

That’s the conclusion one gets from sitting down with Nick Cassavetes, the 6-foot-6, square-jawed, mustachioed, multi-tattooed film director who was so wild and belligerent as a kid that his mother - actress Gena Rowlands - gave him a suitcase for his 16th birthday so he could pack up and move out. Now, a couple of lifetimes later, he has made the film “My Sister’s Keeper,’’ a movie that requires even more Kleenex than his last hit tearjerker, 2004’s “The Notebook.’’

“As a society, we are trained not to feel things. We respect things that are scientific and cerebral, and smart, and this ain’t one,’’ Cassavetes says over water and tea at the Chateau Marmont. His friend, the film’s star, Cameron Diaz, sits across from him, all long legs and scarves and jeans and jewelry.

Throughout the afternoon, the 50-year-old Cassavetes can’t stop showering Diaz with loud, brash adulation, while she looks at him with the fondness one reserves for a beloved papa bear. Diaz focuses on him intently with those limpid eyes, as green-blue as a bay in the Bahamas, and twirls her uncoiffed blond hair with a finger.

The film, based on the Jodi Picoult bestseller, tells the story of a family coping with the elder daughter’s debilitating cancer. As part of the mother’s unbending plan to do everything possible to save the girl, a younger daughter had been conceived to provide bone marrow and other genetic material for the dying teen. As the story progresses, the younger girl (played by Abigail Breslin) sues her parents to stop making her undergo the many medical procedures - in effect, for control of her own body.

“I guarantee you that everyone who read this script saw it as a TV movie, a cushy, sappy tear-jerker,’’ says Diaz, who plays the mother. “But when you say Nick Cassavetes is directing, it changes everything.’’

Cassavetes, the son of famed independent film director John Cassavetes, has been acquainted with Diaz since both shared an agent 15 years ago, when she was just breaking into Hollywood with “The Mask’’ and he was a character actor playing heavies in such films as “Face/Off.’’ He sought out Diaz for the role, even though she’s best known for such broad comedies as “There’s Something About Mary.’’

“We are all aware that Cameron doesn’t have children in real life, and [everyone said], ‘Won’t you hire someone named Kate for this part?’ but I was bored with that,’’ says Cassavetes of the pleas for the reigning queens of dramas, Kate Winslet and Cate Blanchett. “I was like, ‘This girl can do it.’ ’’

“My Sister’s Keeper’’ is undoubtedly a personal story for Cassavetes, who reveals somewhere in the conversation that his oldest daughter, now 23, suffers from a congenital heart defect. “It’s the gift that keeps on giving,’’ he says sarcastically, although he notes that the unexpected wallop of it made him grow up.

He understands the mother character’s single-minded devotion to her child. Cassavetes tells a story about when his daughter was little and had to have an operation for scoliosis, a spine condition that often accompanies such heart defects.

“She had gotten pneumonia and there was a chance she was going to die. They were sticking a tube down her nose and in her lungs every hour and were making her cough. It was very brutal and hard on her, and I could literally see the life sucked out of my daughter.’’ Finally, Cassavetes threw the doctors out. “They were like, ‘You are killing your daughter. She needs these things. She could be dead by morning.’ I said, ‘I want [you] out of the room.’ ’’

His daughter survived the night, and Cassavetes ultimately apologized to the doctors, but, as he points out, “I know what is best for my kid, and I am going to get it. Why? Because that is my job. Why have kids? Because they are pretty to look at? No, you have got to protect them until they get big enough, and then they can protect themselves.’’

“It’s always present with him,’’ Diaz says. “There were moments when we were in a scene and I’d look over, and Nick’s by the camera and he is crying. Tears are coming down his face. That’s how generous he is.’’